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" (see section (n.)). 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.