Early 18th century; earliest use found in Nathan Bailey (d. 1742), lexicographer and schoolmaster. From classical Latin armāmentārium storehouse for military equipment, armoury, arsenal from armāmentum + -ārium.
Definition of armamentary in US English:
armamentary
nounˌɑːməˈmɛnt(ə)ri
Armamentarium.
Origin
Early 18th century; earliest use found in Nathan Bailey (d. 1742), lexicographer and schoolmaster. From classical Latin armāmentārium storehouse for military equipment, armoury, arsenal from armāmentum + -ārium.