c. 1300, "arms and weapons collectively; defensive armor;" see arm (n.2) + -ory. Meaning "place where arms are manufactured" is from mid-15c. (see armor + -y (1)). Also used in a sense of "arsenal" (mid-15c.); the sense of "science of heraldry" (late 15c.) is from Old French armoierie, from armoier "to blazon," from Latin arma "weapons" (see arm (n.2)).