[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., ii. 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.
1873. 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.
