1. Not remaining steadily in the same place; apt to move or be moved about.
a. 1225. Ancr. R., 122. Ne scheaweð heo þet heo is dust, & vnstable þinc, þet mid a lutel wind of a word is anon to blowen.
a. 1340. Hampole, Ps. x. 1. If i doe i sall be like a sparou, þat is, vnstabile and lyght.
1388. Wyclif, Gen. iv. 14. Y schal be vnstable of dwellyng and fleynge aboute in erthe.
1483. Cath. Angl., 357/2. Vn Stabylle, argus, vagus.
1597. R. Tofte, etc., Laura, I. xviii. If Sea no other thing doth shew to bee Than most vnstable waters moouing oft.
1634. Sir T. Herbert, Trav., 91. Sands … in great drifts … so light and vnstable, that the high wayes are neuer certaine.
1653. W. Ramesey, Astrol. Restored, 179. Aries,… though it be a sign fiery, yet is it moveable and unstable.
b. Not steady in position; readily swaying or shaking; liable to swing or fall.
1390. Gower, Conf., I. 200. Now herke how thilke unstable whel, which evere torneth, wente aboute.
1393. Langl., P. Pl., C. XI. 37. Stonde he neuere so styfliche þorgh sterynge of the bote, He bendeþ and boweþ, þe body is vnstable.
c. 1480. Henryson, Fables, Cock & Fox, 199. Thy strenth is nocht, thy stule standis vnstabill.
a. 1542. Wyatt, in Tottel’s Misc. (Arb.), 38. So foloweth me remembrance of that face: That with my teary eyn, swolne, and vnstable, My desteny to beholde her doth me lead.
1567. Gude & Godlie B. (S.T.S.), 106. As quheill vnstabill and caffe befoir the wind.
1600. Fairfax, Tasso, XIX. xiii. When the still windes stirre not th’ vnstable maine.
1736. Thomson, Liberty, IV. 302. On each hand Amazing seen amid unstable waves, The splendid palace shines.
1760. Goldsm., Cit. W., ii. A strange people … who have founded an empire on this unstable element [sc. the ocean].
1857. Buckle, Civilis., vii. 347. The sailor is naturally more superstitious than the soldier, because he has to deal with a more unstable element.
1873. Maxwell, Electr. & Magn., I. 141. The body therefore is unstable even when constrained to move parallel to itself, à fortiori it is unstable when altogether free.
c. Of movement: Unsteady; irregular.
1549. Compl. Scot., vi. 54. It makkis ane onstabil reuolution in thre hundretht xlviij dais.
1819. Scott, Ivanhoe, xlii. Down he came, with an unstable step and a strong flavour of wine.
d. Mech. Of equilibrium (q.v.).
1839. G. Bird, Nat. Philos., 31. The body will be in a state of unstable equilibrium.
1860. All Year Round, No. 69. 450. An acrobat balances a ladder on his shoulder; on the ladder, perhaps will mount a child…. The whole are in unstable equilibrium.
2. Not stable in purpose; vacillating, fickle, changeable.
c. 1290. S. Eng. Leg., I. 319/685. Wrathþe he berth luytel ȝwyle:… Glad and bliþe, and onstable of þat he hath to done.
1297. R. Glouc., 10507. He made of þe olde lawes is chartre atte laste,… & aselede is vaste inou, Ac suþþe as vnstable man wiþ sede & wiþ drou.
c. 1305. Pilate, 183, in E. E. P. (1862), 116. Alle þat ihurde þis cas Wondrede moche of þemperour, þat he vnstable was.
c. 1380. Wyclif, Sel. Wks., II. 10. Þis Emperour … was unstable as watir.
c. 1400. Destr. Troy, 8057. Hit is a propertie apreuit … To all wemen … To be vnstable & not stidfast.
c. 1450. trans. De Imitatione, III. I. 121. Euery man is a lyer, sike, unstable, and slydyng.
c. 1485. Digby Myst. (1882), III. 588. Woman, why art þou so onstabyll?… why art þou a-ȝens god so veryabyll?
1509–10. Act 1 Hen. VIII., c. 11. Many lyght and unstable Persons.
a. 1548. Hall, Chron., Hen. V., 38. The Cambers, otherwise called the vnstable Welshemen.
1607. Shaks., Cor., III. i. 148. It must omit Reall Necessities, and giue way the while To vnstable Slightnesse.
1653. Milton, Ps. v. 25. In his faltring mouth unstable No word is firm.
1661. South, Serm. (1715), III. 192. Such Pretenders may beguile Factious and Unstable Minds.
1791. Wolcot (P. Pindar), Lousiad, III. ix. [A deed] Which Cain perform’d, in godliness unstable.
1855. Macaulay, Hist. Eng., xv. III. 613. His nature, lamentably unstable, was not ignoble.
1891. Farrar, Darkn. & Dawn, xxv. Onesimus was too unstable to withstand the combined temptations by which he was surrounded.
absol. 1582. N. T. (Rhem.), 2 Pet. iii. 16. Certaine things hard to be vnderstoode, which the vnlearned and vnstable depraue.
1630. H. Lynde (title), Via Devia: The By-Way: Mis-leading the weake and vnstable into dangerous paths of Error.
1650. Baxter, Saints’ R., III. xi. § 18. 497. Drawing off the unstable from the doctrine and way of life.
3. Not fixed in character or condition; exposed to vicissitude or chance; apt to change or alter; variable.
c. 1340. Hampole, Pr. Consc., 1420. Þe worlde is swa unstable, Alle þat men sese þar-in es chaungeable.
c. 1375. Lay Folks Mass-Bk. (MS. B.), 390. Þo weders grete & vnstable, Lord make gode.
1387. Trevisa, Higden (Rolls), I. 139. Hap was vnstable and vnstedefast; ones wiþ þat oon side, and eft wiþ þat oþer.
c. 1412. Hoccleve, De Reg. Princ., 705. O lord! þis world vnstabyl is.
c. 1450. trans. De Imitatione, III. lxiv. 149. I finde all vnferme & vnstable, what euere I beholde oute of þe.
1513. Douglas, Æneid, XI. viii. 118. The variant chance Of our onstabill lyfe.
a. 1542. Wyatt, in Tottel’s Misc. (Arb.), 35. Vnstable dreame,… Be stedfast ones, or els at least be true.
a. 1642. Kynaston, Leoline & Sydanis, 141. O wretched state unstable Of mortal men!
1657. in Verney Mem. (1907), 560. These giddy and unstable times.
1768. Boswell, Corsica, ii. 73. The Genoese … were … in an unstable, and perilous condition.
1796. Mme. D’Arblay, Camilla, III. 75. We must allow to our unstable virtues all the encouragement that can prop them. Ibid., V. 540. The perpetual vicissitudes of our unstable condition.
1829. Hood, Eugene Aram, 46. Or is it some historic page Of kings and crowns unstable?
1863. H. Cox, Instit., III. iii. 628. That all oligarchies and democracies are unstable.
1884. Church, Bacon, ix. 223. English seemed to him too homely to express the hopes of the world, too unstable to be trusted with them.
b. spec. in Chem.
1849. D. Campbell, Inorg. Chem., 216. Its [sc. suboxide of copper] salts are very unstable.
1857. Miller, Elem. Chem., Org., 59. Grape sugar forms definite but unstable combinations with the alkaline bases.
1890. Retrospect Med., CII. 2. The chloral hydrate is, comparatively, an unstable compound.
4. Not firm or solid; insecure.
1565. Jewel, Repl. Harding (title-p.), The Weake and vnstable Groundes of the Romaine Religion.
1613. Purchas, Pilgrimage (1614), 597. The Earth was couered with sand, which yeelded an vnstable footing.
