From the second edition (1989):
(ɪmædʒɪˈneɪʃən) Also 4–6 with y for i and -cio(u)n, etc.; 6–7 immagination. [a. F. imagination (12th c.), ad. L. imāginātiōn-em, noun of action from imāginārī, -āre to imagine.]

1. The action of imagining, or forming a mental concept of what is not actually present to the senses (cf. sense 3); the result of this process, a mental image or idea (often with implication that the conception does not correspond to the reality of things, hence freq. vain (false, etc.) imagination).

a1340 Hampole Psalter xxxvii. 7 Þe fende þat‥trauails my saule in vayn ymagynaciouns. 1377 Langl. P. Pl. B. xx. 33 Wenynge is no wysdome ne wyse ymagynacioun. 1450–1530 Myrr. our Ladye 41 Anon ymaginacions of the same thynges come to his mynde. c1460 Fortescue Abs. & Lim. Mon. ix. (1885) 128 We nede in this case to vse coniecture and ymaginacion. 1576 Fleming Panopl. Epist. 193 They‥accounted his undoubted divinations, madde immaginations. 1690 Locke Hum. Und. iii. v. §12 When we speak of Justice, or Gratitude, we frame to our selves no Imagination of any thing existing. 1761 Hume Hist. Eng. III. xlv. 8 note, Could such an imagination ever have been entertained by him? 1829 Jas. Mill Hum. Mind (1869) I. vii. 239, I am said to have an imagination when I have a train of ideas. 1896 Duke of Argyll Philos. Belief 223 The truths which they proclaimed were facts and not imaginations.

2. The mental consideration of actions or events not yet in existence. a. Scheming or devising; a device, contrivance, plan, scheme, plot; a fanciful project. Obs. exc. as a biblical archaism.

c1385 Chaucer L.G.W. 1523 Hypsip., With-outen any othir affeccioun Of loue or euyl ymagynacyoun. c1400 Mandeville (1839) xxiii. 251 Alle here lust and alle here Ymaginacioun is for to putten alle Londes undre hire subieccioun. 1535 Coverdale Lam. iii. 60 Thou hast herde their despytefull wordes (O Lorde) yee and all their ymaginacions agaynst me. 1548 Hall Chron., Rich. III 47b, That mischevous ymaginacion whiche he nowe newely beganne and attempted. 1660 Trial Regic. 9 In no Case else Imagination, or Compassing, without an actual effect of it, was punishable by our Law. 1709 Swift Advancem. Relig. Wks. 1755 II. i. 117 These airy imaginations of introducing new laws for the amendment of mankind. 1760–72 H. Brooke Fool of Quality (1809) III. 47 Any imagination‥tending to change the nature or form of any one of the three estates.

b. Impression as to what is likely; expectation, anticipation. Obs.

1623 Bingham Xenophon 29 As soone as it was day, all set forward‥imagining that by sun-set they should reach to Villages of the Babylonian Territorie. Neither were they deceiued in their imagination. 1628 Hobbes Thucyd. (1822) 106 The sickness—the only thing that exceeded the imagination of all men. 1654 Marvell Corr. Wks. 1872–5 II. 11 To tell you truly mine own imagination, I thought he would not open it while I was there.

3. That faculty of the mind by which are formed images or concepts of external objects not present to the senses, and of their relations (to each other or to the subject); hence frequently including memory. (Sometimes called the ‘reproductive imagination’; cf. sense 4.)

1340 Ayenb. 158 Oþerhuil hit is ase to þe þoȝte, oþer ase to þe ymaginacion. 1398 Trevisa Barth. De P.R. iii. vi. (Tollem, MS.), The þridde hat ymaginacion: þerby þe soule biholdeþ þe liknesse of bodily þingis þat beþ absente. 1485 Caxton Chas. Gt. 1 The comune understondyng is better content to the ymagnacion local. 1541 Copland Guydon's Quest. Chirurg. Ejb, In the fyrste parte of the ventricle before is put ye common blode. In the seconde ye vertue of ymagynacyon. 1601 Shakes. All's Well i i. 93, I haue forgott him. My imagination Carries no fauour in't but Bertrams. 1639 T. Brugis tr. Camus' Mor. Relat. 320 The very features of the faces‥remained so ingraven in his imagination. 1751 Harris Hermes Wks. (1841) 219 We have‥a faculty called imagination or fancy‥which retains the fleeting forms of things, when things themselves are gone, and all sensation at an end. 1797 Mrs. Radcliffe Italian i. (1826) 5 The beauty of her countenance haunting his imagination. 1840 Mill Diss. & Disc., Bentham (1859) I. 353 The Imagination‥to which the name is generally appropriated by the best writers of the present day [is] that which enables us, by a voluntary effort, to conceive the absent as if it were present.

4. The power which the mind has of forming concepts beyond those derived from external objects (the ‘productive imagination’). a. The operation of fantastic thought; fancy.

c1386 Chaucer Miller's T. 426 Men may dyen of ymaginacion So depe may impression be take. 1390 Gower Conf. III. 98 (MS. Fairfax 3) Full of ymaginacion, Of dredes and of wrathfull þoghtes. 1601 Shakes. Twel. N. ii. v. 48 Looke how imagination blowes him. 1645 Boate Irel. Nat. Hist. (1652) 75 As if in very deed he had‥seen and suffered all those things, which his weak imagination‥did figure unto him. 1834 Medwin Angler in Wales I. 275 And I fancied, though it might be imagination, that her's trembled too.

b. The creative faculty of the mind in its highest aspect; the power of framing new and striking intellectual conceptions; poetic genius.

1509 Hawes Past. Pleas. xiv. (Percy Soc.) 53 Upon hys ymaginacyon He made also the tales of Caunterbury. 1590 Shakes. Mids. N. v. i. 14 And as imagination bodies forth The forms of things vnknowne; the Poet's pen Turnes them to shapes, and giues to aire nothing, A locall habitation, and a name. 1657 R. Ligon Barbadoes (1673) 19 Nor can imagination frame so great a beauty. 1762 Kames Elem. Crit. (1833) 480 This singular power of fabricating images without any foundation in reality, is distinguished by the name of imagination. 1871 Darwin Desc. Man I. ii. 45 The Imagination is one of the highest prerogatives of man. By this faculty he unites, independently of the will, former images and ideas, and thus creates brilliant and novel results.

5. The mind, or a department of the mind, when engaged in imagining; hence, the operation of the mind generally; thinking; thought, opinion. Now rare or Obs.

c1384 Chaucer H. Fame ii. 220, I wille Tellen the a propre skille, And worthe a demonstracion In myn ymagynacion. 1390 Gower Conf. III. 303 Now is she red, now is she pale, Right after the condition Of her ymagination. c1500 Three Kings Sons 138 The kynge‥in his ymaginacion thought to make a grete assaute vpone the Turkes loggyng. 1548 Hall Chron., Edw. IV 239b, Conjectures, which as often deceyve the imaginacions of fantastical folke. 1632 J. Hayward tr. Biondi's Eromena 12 That neither she‥nor others‥came thereby to lose or gaine in the imagination of others. 1662 J. Davies tr. Olearius' Voy. Ambass. 181 Upon the first sight thereof, it run into our imagination, that they were the Cosaques.

6. attrib. and Comb., as imagination-consciousness, imagination-game, imagination-image, imagination-mill, imagination-monger, imagination-process, imagination-world; imagination-liberating, imagination-manufactured, imagination-stirring, imagination-stunning adjs.

1901 E. B. Titchener Exper. Psychol. I. i. 1 An *imagination-consciousness, our mind as it is when we are imagining something. 1926 E. Bowen Ann Lee's, & Other Stories 53 But the *imagination-game palled upon him. 1890 W. James Princ. Psychol. II. xviii. 50 *Imagination-images‥feel subject to our spontaneity [etc.]. 1933 R. Tuve Seasons & Months i. 28 It was not the *imagination-liberating concept of Nature. 1902 North Amer. Rev. Dec. 768 The [Christian] Science‥secures to him life-long immunity from *imagination-manufactured disease. 1899 Harper's Mag. Dec. 40/1 His *imagination-mill was hard at work in a minute. 1889 Pall Mall G. 28 June 3/2 To the exclusion of other industrious *imagination-mongers. 1890 W. James Princ. Psychol. II. xviii. 72 The *imagination-process can then pass over into the sensation-process. In other words, genuine sensations can be centrally originated. 1892 ‘Mark Twain’ Amer. Claimant x. 88 The *imagination-stunning material development of this century. 1904 Daily Chron. 19 Oct. 8/1 This glimpse into the *imagination-world of London.