1690s, from tri- "three" + Latin sectus "cut," past participle of secare "to cut" (from PIE root *sek- "to cut"). Probably patterned on bisect. Related: Trisected; trisecting; trisection (1660s).
trisect a line
tripod
Tripoli
triptych
trireme
Triscuit
trisect
trisexual
triskaidekaphobia
triskelion
trismus
trisomy
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