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).
Entries linking to trisect
tri-
word-forming element meaning "three, having three, once every three," from Latin tres (neuter tria) or Greek treis, trias "three" (see three).
*sek-
Proto-Indo-European root meaning "to cut." It forms all or part of: bisect; dissect; hacksaw; insect; intersect; resect; saw (n.1) "cutting tool;" Saxon; scythe; secant; secateurs; sect; section; sector; sedge; segment; skin; skinflint; skinny; transect.
It is the hypothetical source of/evidence for its existence is provided by: Hittite shakk- "to know, pay attention to;" Latin secare "to cut," sectio "a cutting, cutting off, division;" Old Church Slavonic seko, sešti "to cut," sečivo "ax, hatchet," Russian seč' "to cut to pieces;" Lithuanian įsėkti "to engrave, carve;" Albanian šate "mattock;" Old Saxon segasna, Old English sigðe "scythe;" Old English secg "sword," seax "knife, short sword;" Old Irish doescim "I cut."
bisect v.
"to cut in two," 1640s, from Modern Latin bisectus, from Latin bi- "two" (see bi-) + secare "to cut" (from PIE root *sek- "to cut"). Related: Bisected; bisecting.