Defn: An ancient anthem, — usually known by its Latin name tersanctus.See Tersanctus.

TRISECT
Tri*sect", v. t. [imp. & p. p. Trisected; p. pr. & vb. n.
Trisecting.] Etym: [Pref. tri- + L. sectus, p. p. of secare to cut.
See Section.]

1. To cut or divide into three parts.

2. (Geom.)

Defn: To cut or divide into three equal parts.

TRISECTED
Tri*sect"ed, a. (Bot.)

Defn: Divided into three parts or segments by incisions extending to the midrib or to the base; — said of leaves.

TRISECTION
Tri*sec"tion, n. Etym: [Cf. F. trisection.]

Defn: The division of a thing into three parts, Specifically: (Geom.) the division of an angle into three equal parts.

TRISERALOUS
Tri*ser"al*ous, a. Etym: [Pref. tri- + sepal.] (Bot.)