mid-14c., "marshal (troops), arrange (an army for battle);" late 14c., "put (things) in order, arrange; get (something) ready, prepare; equip, fit out, put clothing on; adorn, decorate," from Old French areyer, earlier areer "to put in order," from Vulgar Latin *ar-redare "put in order" (source also of Italian arredare), from Latin ad "to" (see ad-) + *redum, from Frankish *ræd- "ready" or some cognate Germanic source, from Proto-Germanic *raidjan "to place in order" (source also of Gothic garadis, Old English geræde "ready;" see ready (adj.)). Related: Arrayed; arraying.
mid-14c., "order or position of things, arrangement, sequence," from Anglo-French arrai, Old French aroi, arroi (12c.), from areer "to put in order" (see array (v.)). From late 14c. as "rank or line of soldiers; troops drawn up in battle formation," also "equipment, furnishings, gear; splendid furnishings, grandeur, magnificence." Meaning "an orderly assemblage" is from 1814.