c. 1400, "an armed force," from Latin armatura "armor, equipment," from armatus, past participle of armare "to arm, furnish with weapons" from arma (see arm (n.2)). Meaning "armor" is mid-15c.; that of "protective covering of a plant or animal" is from 1660s. Electromagnetic sense is from 1835.[armature etymology, armature origin, 英语词源]