From the second edition (1989):
whence, adv., conj. (n.)
(hwɛns) Forms: 4–5 whannes, whennes, (4 huannes, wannes, whennus, -ys), 4–6 whens, 5 qwens, 6 whense, Sc. quhens, quhence, 6– whence. [13th c. ME. whannes, whennes, f. whanne, whenne + -s suffix1. In all senses often preceded by redundant from, †fro (from 15a), occas. of (obs. or arch.).]

I. Interrogative uses. (Now replaced in ordinary colloquial speech by where…from.)

1. From what place? a. in a direct question.

a1300 K. Horn 161 (Camb. MS.) Whannes beo ȝe, faire gumes, þat her to londe beoþ icume. 1382 Wyclif Gen. xvi. 8 Whens comyst thow, and whithir gost thow? c1430 Syr Tryam. 431 What do ye here, madam? Fro whens come ye? [ed. Copland (c 1550) Of whens be you‥?]. 1526 Tindale John vi. 5 Whence shall we bye breed that these might eate? 1540 Palsgr. Acolastus ii. v. Nij, From whense haste thou brought hym hyther? 1547 Boorde Introd. Knowl. xxvii. (1870) 192 Of whens be you? I am of England. 1596 Shakes. Tam. Shr. ii. i. 103 Of whence, I pray? Tra. Of Pisa, sir. 1697 Dryden Æneis x. 945 Whence am I forc'd, and whether am I born? 1720 Delany News fr. Parnass. 19 From whence is this Fool? 1773 Goldsm. Stoops to Conq. v, My wife, as I'm a Christian. From whence can she come? 1855 Tennyson Brook 22 O babbling brook,‥Whence come you?

b. in an indirect question.

c1300 St. Brandan 288 We nuteth noȝt bote thurf God whannes hit is i-brouȝt. 1377 Langl. P. Pl. B. v. 532 Þis folke frayned hym firste fro whennes he come. c1450 Merlin 44 They axed hym of whens he was. 1526 Tindale John ix. 29 Thys felowe, we knowe not from whence he ys. 1579 Spenser Sheph. Cal. May 261 The Kidd‥Asked‥who, and whence that he were. 1697 Dryden Æneis vi. 1193 He‥ask'd his airy Guide, What, and of whence was he. Ibid. viii. 150 Resolve me, Strangers, whence, and what you are. 1710 De Foe Ess. Public Credit 6 We‥hardly know whence it [sc. the wind] comes, or whither it goes. 1802 M. Edgeworth Moral T., Forester v, He inquired whence the water came. 1886 Stevenson Kidnapped xxv, There was no question put of whence I came or whither I was going.

2. gen. and transf. From what source, origin, or cause? a. in a direct question.

c1305 Pop. Treat. Sci. (1841) 139 Loke hou crokede thu were ther,‥Whannes [earlier text Fra ȝwam] cometh hit siththe to bere the so heȝe? 1382 Wyclif Matt. xxi. 25 Of whennes was the baptem of Joon; of heuene, or of men? 1526 Tindale Luke i. 43 Whens hapeneth this to me, that the mother off my lorde shulde come to me? 1697 Dryden Æneis x. 9 From whence these Murmurs, and this change of Mind? 1759 Sterne Tr. Shandy II. xvii, But whence‥have you concluded‥that the writer is of our church? 1853 Dickens Bleak Ho. xix, From whence have we derived that spiritual profit?

b. in an indirect question.

1485 Caxton Chas. Gt. 53, I am wel admeruaylled fro whens that cometh to the suche presumpcion to speke so hastyly. 1599 Broughton's Lett. viii. 28 There are some that can tell‥from whence you borrow‥your much bragd~of Concent. 1667 Milton P.L. v. 856 Strange point and new! Doctrin which we would know whence learnt. 1718 Prior Solomon i. 459 Ask Reason now, whence Light and Shade were giv'n. 1781 Cowper Truth 237 An apt similitude shall show Whence springs the conduct that offends you so. 1849 C. Brontë Shirley vii, The laughter and mirth of her uncle, and Hannah, and Mary, she could not tell whence originating. 1859 Tennyson Pelleas & Ettarre 520 For so the words were flash'd into his heart He knew not whence or wherefore. 1867 F. Harrison in Questions Ref. Parlt. 255 No man can say from whence the greater danger to order arises.

II. Relative or conjunctive uses.

3. From which place; from or out of which.
Also with ellipsis of there or thither in the main clause.

1382 Wyclif Ps. cxx[i]. 1, I rered vp myn eȝen in to the mounteynes; whennys [1388 fro whannus] shal come helpe to me. 1535 Coverdale Deut. xi. 10 The londe of Egipte, whence ye came out. 1560 Bible (Geneva) Isa. li. 1 Loke vnto the rocke, whence ye are hewen. a1700 Evelyn Diary 30 June 1644, A dreadfull cliff, from whence the country and river yeald a most incomparable prospect. 1728–46 Thomson Spring 910 Mossy rocks, Whence on each hand the gushing waters play. 1838 Dickens O. Twist xxxiv, The little room‥looked into a garden, whence a wicket-gate opened into a small paddock. 1887 Swinburne Stud. Prose & Poetry (1894) 141 The quarter from whence the following lucubration is addressed.
1590 Shakes. Com. Err. iii. i. 37 Let him walke from whence he came. 1591 —— Two Gent. ii. iv. 122 Now tell me: how do al from whence you came? 1611 Bible Job x. 21 Let me alone that I may take comfort a litle, Before I goe whence [Coverdale thyther, from whence] I shall not returne.

b. as compound relative: From the place in which, from where. poet. Obs. rare.

1601 Shakes. All's Well iii. ii. 124 Come thou home Rossillion, Whence honor but of danger winnes a scarre, As oft it looses all. 1607 —— Timon i. i. 22 Our Poesie is as a Goume [printed Gowne] which vses [i.e. oozes] From whence 'tis nourisht.

4. gen. and transf. From which source or origin (as a product); from which cause (as a result); from which fact or circumstance (as an inference).

a1568 R. Ascham Scholem. i. (Arb.) 61 This opinion is not French, but plaine Turckishe: from whens, som French fetche moe faultes, than this. 1590 Spenser F.Q. iii. iii. 1 Vertue‥Whence spring all noble deeds and neuer dying fame. 1678 Cudworth Intell. Syst. 32 To lay down such Principles, as from whence it would follow, that any Real Entity in Nature did come from Nothing and go to Nothing. 1731–8 Swift Pol. Conversat. Introd. 29 From whence I did then conclude‥that Wine doth not inspire Politeness. 1781 Cowper Expost. 111 Faith, the root whence only can arise The graces of a life that wins the skies. 1859 Jephson Brittany vi. 81 St. Ive‥became a successful advocate, whence he is now venerated by Breton lawyers as their patron. 1885 G. L. Goodale Physiol. Bot. 400 During its revolution a tip bows or nods successively to all points of the compass; whence the name nutation.

III. 5. as n. (nonce-use.) That from which something comes or arises; place of origin; source.

1832 Motley in Corr. (1889) I. 18, I was summoned before the Senate of the University, and then wrote my name and my whences and whats, etc., etc., in a great book. 1869 Mrs. Whitney Hitherto xviii. 242 We start from some whence, and are expressed through to somewhere. 1875 E. White Life in Christ i. iv. (1878) 30 Uncertain as to the Whence and Whither of humanity.