c. 1300, "to fit out, equip; to dress in finery, to adorn," from Old French atirier "to equip, ready, prepare," from a- "to" + tire "order, row, dress" (see tier). Related: Attired; attiring.
attire (n.)
c. 1300, "equipment of a man-at-arms; fine apparel," from attire (v.).