cusp
(kʌsp)
[ad. L. cuspis, cuspid-em point.]
1. Astrol. The beginning or entrance of a ‘house’.
| 1585 Lupton Thous. Notable Th. (1675) 165 Whosoever hath any fixed Star of the first Honour or Magnitude..in the Degree of their Cuspe, of the tenth House. 1647 Lilly Chr. Astrol. iv. 33 The Cusp or very entrance of any house, or first beginning. 1651 Culpepper Astrol. Judgem. Dis. (1658) 47 In this figure Capricorn is upon the cuspe of the ascendent. 1815 Scott Guy M. iii, Houses of heaven, with their cusps, hours, and minutes; Almuten, Almochoden, Anabibazon, Catabibazon. 1856 Vaughan Mystics II. 51 Reckoning the cusps and hours of the houses of heaven! |
2. gen. A point, pointed end, apex, peak; an ornament of a pointed form.
| 1647 H. More Song of Soul ii. App. lxvii, The Cuspe of the Cone. 1847 Sir H. Taylor Minor Poems Wks. 1864 III. 232 And mid the loftiest [mountains] we could well discern One that was shining in a cusp of snow. 1876 Rock Text. Fabr. vi. 59 Stopped with graceful cusps and artichokes. |
† b. erroneously: Top, surface.
| 1658 R. Franck North. Mem. (1821) 61 That bush, whose slender branches wantonly dangle sporting themselves on the cusp of the water. |
3. Astron. Each of the pointed extremities or ‘horns’ of the crescent moon (or of Mercury and Venus); also of the sun when partially eclipsed.
| 1676 Halley in Rigaud Corr. Sci. Men (1841) I. 229, 70 degrees from the northern cusp [of the moon], then something obtuse. 1764 Phil. Trans. LIV. 106 About the middle of the eclipse, the air was very clear, and the cusps well defined. 1793 Herschel in Phil. Trans. LXXXIII. 202 One cusp of Venus appearing pointed, and the other blunt. |
4. Geom. A point at which two branches of a curve meet and stop, with a common tangent; or at which the moving point describing the curve has its motion exactly reversed. Called also spinode or stationary point. (Also applied to an analogous point on a curved surface.)
| 1758 I. Lyons Treat. Fluxions vii. §191. 142 A point of Reflection or Cusp. 1857 Whewell Hist. Induct. Sc. II. 362 The peculiar inflected form of the wave surface, which has what is called a cusp. 1875 Todhunter Diff. Calc. (ed. 7) xxii. §301 If the two branches lie on opposite sides of the common tangent, the cusp is said to be of the first species; if on the same side, the cusp is said to be of the second species..Cusps of the first species have been called ‘keratoid’ cusps, and of the second ‘rhamphoid cusps’. |
5. Arch. Each of the projecting points between the small arcs or ‘foils’ in Gothic tracery, arches, etc.
| 1813 Sir J. Hall Ess. Gothic Archit. 32 In all the concave bends of the stone-work, a small pointed ornament occurs, which is very common in Gothic windows..I have ventured to apply to it [the name] of cusp, by which mathematicians denote a figure of this sort. 1845 Ecclesiologist IV. 20 Ball-flowers, mouldings, feathered cusps, and other decorative detail. |
6. Anat. a. A projection or protuberance upon the crown of a tooth: cf. cuspidate. b. Any pointed projection or extremity, as of the valves of the heart.
| 1849–52 Todd Cycl. Anat. IV. 921/1 The four principal cusps..are more pointed and prolonged than in Man. 1872 Mivart Elem. Anat. vii. (1873) 252 The sixth and seventh teeth of the lower jaw are called true molars. Each bears five cusps. 1878 T. Bryant Pract. Surg. I. 301 The valve cusps being unable to meet and close the canal. |
7. Bot. A pointed end of any organ; esp. a sharp rigid point of a leaf.
| 1870 Hooker Stud. Flora 319 Leaves opposite hastate⁓deltoid with horizontal cusps. Ibid. 328 Euphorbia amygdaloides..cusps of glands converging. |