1560s, "section of a circle between two radii," from Late Latin sector "section of a circle," in classical Latin "a cutter, one who cuts," from sectus, past participle of secare "to cut" (from PIE root *sek- "to cut"). Translated Greek tomeus in Latin editions of Archimedes. Meaning "area, division" appeared 1920, generalized from military sense (1916) of "part of a front," based on a circle centered on a headquarters. As a verb from 1884. Related: Sectoral; sectorial.