From the second edition (1989):
[un-1 12 and 5b.]

1. a. The quality of being uncertain in respect of duration, continuance, occurrence, etc.; liability to chance or accident. Also, the quality of being indeterminate as to magnitude or value; the amount of variation in a numerical result that is consistent with observation.
For the phrase the glorious uncertainty of the law see glorious a. 5b.

1382 Wyclif 1 Tim. vi. 17 Nethir for to hope in vncerteynte of richessis, but in quyk God. 1495 Act 11 Hen. VII, c. 36 Preamble, Greate uncertente and troble myght her~after growe bytwyne the seid Duches and the seid nowe Duke. 1526 Pilgr. Perf. (W. de W. 1531) 230 Bothe for the vncertaynty of the same [life], and also for the paynfulnes‥therof. a1548 Hall Chron., Hen. IV, 20 Whose study was euer to procure malice, and to set al thynges in broile and vncertentie. a1586 Sidney Arcadia ii. xxvi. (1912) 318 The uncertainty of his estate made you take armes. 1617 Moryson Itin. i. 278 By reason of the aforesaid uncertaintie in receiving money by billes of exchange. 1677 A. Yarranton Eng. Improv. 19 Such hazards at Sea as attend Merchants, with the badness and uncertainty of Personal Security. 1755 Earl of Corke in J. Duncombe Lett. (1773) III. 29 The uncertainty of the weather was still more surprising than the cold: we have had all kinds of seasons in a day. 1794 R. J. Sulivan View Nature I. 164 There is, besides this, great uncertainty of colour, according as the heat varies. 1810 Scott Lady of L. iii. ii, Neither broken nor at rest; In bright uncertainty they lie. 1853 Proc. R. Irish Acad. V. 372 As to the sun and moon, it is more doubtful. In the transit they have larger probable errors than the stars. For the sun I obtained‥the first limb ±0s·116, the second ±0s·087;‥while stars‥had but ±0s·097. This greater uncertainty arises from the strong contrast between the bright and dark surfaces whose boundary we take. 1860 Tyndall Glac. i. xi. 75 The uncertainty of the footing between the blocks of ice. 1861 G. B. Airy Theory Errors of Observations i. 4 Strictly speaking, we ought‥to use the word ‘uncertainty’ instead of ‘error’. For we cannot at any time assert positively that our estimate or measure, though fallible, is not perfectly correct; and therefore it may happen that there is no ‘error’, in the ordinary sense of the word. 1930 Ruark & Urey Atoms, Molecules & Quanta xviii. 619 If a coordinate q is measured with an error of the order Δq, the uncertainty, Δp, of the conjugate momentum introduced by our measurement is such that Δq·Δph. 1943 M. W. White et al. Practical Physics i. 12 As applied to the final result of a measurement, the accuracy is expressed by stating the uncertainty of the numerical result, that is, the estimated maximum amount by which the result may differ from the ‘true’ or accepted value. 1974 G. Reece tr. Hund's Hist. Quantum Theory xii. 161 We thus have the relationship ∆ Eth between the uncertainty in the determination of energy and the evaluation of a point in time. 1975 Physics Bull. Apr. 165/2 The PTB developed a new measuring apparatus capable of accurate measurements of diameter on pistons of 850 mm and cylinders up to 1200 mm in diameter. The uncertainty in Q, dQ/Q, was estimated to be 3 × 10−5.

b. With a and pl. Something of which the occurrence, result, etc., is uncertain.

1619 in Foster Eng. Factories India (1906) I. 174, I send him not uppon uncertayntyes but uppon sure grounds. 1653 J. Hall Paradoxes 37 We love to toyl for uncertainties, and in this are worse then children. 1691 Andros Tracts II. 251 Most of the Persons in our Government understand little or nothing of Trade, and so they leave it always at uncertainties. 1712 Lady M. W. Montagu Let. to Mr. W. Montagu 9 Dec., I would not advise you to neglect a certainty for an uncertainty. 1757 Pitt in 10th Rep. Hist. MSS. Comm. App. I. 214 Exposed to the most alarming Uncertainties. 1782 F. Burney Cecilia iii. ix, Mr. Arnott was wretched from a thousand uncertainties. 1846 A. Marsh Father Darcy II. viii. 141 Every thing seems so certain, so inevitable, a consequence of the enterprise—yet my mind is harassed by uncertainties. 1864 Bowen Logic xiii. 443 The probability‥of two independent uncertainties happening conjointly.

c. An uncertain gain or emolument.

1650 Greaves Seraglio 168 He hath then but a thousand aspars a day, as the Cadeeleschers have‥; howbeit their uncertainties amount alwayes to a far greater matter.

2. a. The state of not being definitely known or perfectly clear; doubtfulness or vagueness.

c1380 Wyclif Sel. Wks. II. 133 Þat sum men graunten and sum men denyen, for uncerteynte of þe dede. 1395 Purvey Remonstr. (1851) 47 The multitude and vncertaynte of siche lawis. 1565 Cooper Thesaurus, Incertum,‥doubtfulnesse: vncertaintie. 1599 Hakluyt Voy. II. Pref. *4b, Besides the foresaid vncertaintie, into what dangers and difficulties they plunged themselues‥I tremble to recount. a1633 Austin Medit. (1635) 95 This is the briefe of the uncertainty of the History. 1696 Whiston The. Earth iii. (1722) 285, I might‥leave the following Conjectures to the same State of Uncertainty they have hitherto been in. 1765 Museum Rust. IV. 291 The uncertainty in which of the stages the delineation of the plant has been taken. 1802 T. Thomson Chem. ii. v. II. 189 He acknowledged‥that there were two sources of uncertainty, which rendered his conclusions not altogether to be depended upon. 1869 Froude Short Stud. Ser. ii. Educ. (1871) 322 So far as our special occupations go, there is no uncertainty. 1902 J. Gairdner Eng. Ch. 16th Cent. viii. 141 The name of the celebrant was kept a profound secret, and to this day it is a matter of uncertainty.

b. Law. In phr. bad, or void, for uncertainty.

1818 Cruise Digest (ed. 2) IV. 298 Where the words of a deed are so uncertain that the intention of the parties cannot be discovered, the deed will be void. Thus a gift‥to one of the children of J. S., he having four children, is void for uncertainty. 1890 Sir A. Charles in Law Times Rep. LXIII. 767/1 There is some variation in the mode in which the custom is stated, but not enough to make it bad for uncertainty.

c. Something not definitely known or knowable; a doubtful point.

1387 Trevisa Higden (Rolls) II. 377 It is vncerteynte whiche Mercurius þis was. 1577 tr. Bullinger's Decades (1592) 24 What‥is more euident than that which‥no man doeth referre to darkenesse and vncertainties. 1590 Shakes. Com. Err. ii. ii. 187 Vntill I know this sure vncertaintie, Ile entertaine the free'd [sic] fallacie. 1653 W. Ramesey Astrol. Restored 38 To what end‥is it for a man to busie his head about such uncertainties. 1878 Stanley Addr. & Serm. U.S. iii. (1883) 141 Many a one‥has been perplexed by the uncertainties and contentions of history. 1889 Renan's Bk. Job p. xxxix, There is but one remedy for such uncertainties.

3. a. The state or character of being uncertain in mind; a state of doubt; want of assurance or confidence; hesitation, irresolution.

1548 Elyot, Suspensio, a hangyng vp; also doubte or vncertayntee of the mynde. 1598 R. Bernard tr. Terence, Phormio iv. iii, Let me vnderstande‥if they will giue me her, that I may let this alone, least I stay in an vncertaintie. 1607 Shakes. Cor. iii. iii. 124, I banish you, And heere remaine with your vncertaintie. Let euery feeble Rumor shake your hearts. 1635 D. Dickson Expl. Hebr. x. 242 Doeth not this Exhortation importe the Elects vnsetlednesse, and vncertayntie of perseverance? 1746 Wesley Princ. Methodist 43 When I have been in great distress of soul, or in utter uncertainty how to act in an important case. 1794 Mrs. Radcliffe Myst. Udolpho i, She was compelled to rest in uncertainty. 1851 Hawthorne Ho. Sev. Gables ix, Pacing the room‥with the uncertainty that characterized all his movements. 1879 Lubbock Addr. Pol. & Educ. iii. 57 Uncertainty as to the educational value of Science.
pl. 1846 A. Marsh Father Darcy II. viii. 139, I marvel at‥these hesitations and uncertainties in a man of your resolution. 1851 Carlyle Sterling ii. iii, I suppose, he was full of uncertainties.

b. In phr. at uncertainty, upon uncertainties.

1668 Howe Bless. Righteous (1825) 267 Though he be upon great uncertainties as to his enjoyment of them. 1690 Locke 2nd Let. Toleration Wks. 1714 II. 272 Whereby we are as much still at Uncertainty, as we were before, who those are who‥are to be punished.

4. Econ. (The quality of) a business risk which cannot be measured and whose outcome cannot be predicted or insured against (see quots. 1921 and 1964). Cf. risk n. 2a.

1921 F. H. Knight (title) Risk, uncertainty and profit. Ibid. i. 20 A measurable uncertainty, or ‘risk’ proper, as we shall use the term, is so far different from an unmeasurable one that it is not in effect an uncertainty at all. We shall accordingly restrict the term ‘uncertainty’ to cases of the non-quantitative type. It is this ‘true’ uncertainty‥which forms the basis of a valid theory of profit. 1929 G. O'Brien Notes on Theory of Profit ii. 17 The assumption of uncertainty is therefore a disutility and must be rewarded. Is uncertainty bearing on this account, entitled to rank as a separate factor of production. 1964 Gould & Kolb Dict. Social Sci. 606/1 In its broadest definition the term uncertainty is used by economists to refer to any situation in which a set of alternative outcomes is not fully predictable. 1969 D. C. Hague Managerial Economics vii. 137 To conform to established terminology we shall, from now on, use the word uncertainty to mean the same thing as non-insurable risk.

5. (Heisenberg's) uncertainty principle (Physics), a principle of quantum mechanics implying that certain pairs of observables (e.g. the momentum and position of a particle, the energy and lifetime of a quantum level) cannot both be precisely and simultaneously known, and that as one of any pair is more exactly defined, the other becomes more uncertain. Also transf. Cf. Heisenberg, principle of indeterminacy s.v. indeterminacy b.
The principle is usually stated as an inequality such that the product of the uncertainties of the pair of observables cannot be less than a quantity of the order of Planck's constant.

[1928 Physical Rev. XXXII. 570 The principle of uncertainty is particularly clear in this [sc. Weyl's] system.] 1929 Condon & Morse Quantum Mech. i. 21 (heading) The quantum uncertainty principle. 1931 Times Lit. Suppl. 5 Nov. 852/4 Perhaps the most remarkable discovery that has been made in connexion with atomic theory is the so-called Uncertainty Principle. 1955 W. Heisenberg in W. Pauli Niels Bohr 15 It was now [sc. in 1927] assumed in quantum mechanics that real states can always be represented as vectors in Hilbert space (or as ‘mixtures’ of such vectors). The uncertainty principle was the simple expression for this assumption. 1977 Time 14 Mar. 74/1 Even in the age of the Uncertainty Principle and culture fracture, Warren has not lost his sense of life as a sustained drama. 1982 A. M. Lesk Introd. Physical Chem. x. 309 What Heisenberg's uncertainty principle asserts is that for no state of any system can all dynamical variables be arbitrarily well-determined.