[f. TRI- + L. sect-, ppl. stem of secāre to cut, after BISECT.] trans. To divide into three equal parts (esp. in Geom.); sometimes gen. to divide into three parts.
1695. Alingham, Geom. Epit., 44. Trisect any side … in the points d and e.
a. 1696. Scarburgh, Euclid (1705), 88. From hence ’tis manifest, how to trisect a Right angle.
1786. Phil. Trans., LXXVI. 16. Mr. Graham … perceived … how very much more easy a given line was to bisect than to trisect or quinquesect.
1822. De Quincey, Confess., 146. Could not I have reduced it a drop a day, or by adding water, have bisected or trisected a drop?
1876. A. J. Evans, Through Bosnia, ii. 48. We found the dwelling-houses trisected into a sleeping-room, a kitchen, and a store-room.
Hence Trisected ppl. a. (in Bot. = TRISECT a.); Trisecting vbl. sb.
1694. Phil. Trans., XVIII. 70. So the halving, trisecting, quartering, &c. is performed by extracting the Square Root, the Cubick, Biquadratick Roots, &c. of the Terms.
1809. Cavendish, ibid., XCIX. 227. In trisecting, the greatest error we are liable to does not exceed that of bisection in a greater proportion than that of 4 to 3.
1828. Webster, Trisected, divided into three equal parts.
1866. Treas. Bot., 1174. Trisected, cut deeply into three parts.
