early 14c., "make straight; direct, guide, control, prepare for cooking," from Old French dresser, drecier "raise (oneself), address, prepare, lift, raise, hoist, set up, arrange, set (a table), serve (food), straighten, put right, direct," from Vulgar Latin *directiare, from Latin directus "direct, straight" (see direct (v.)).
Sense of "decorate, adorn" is late 14c., as is that of "put on clothing." Original sense survives in military meaning "align columns of troops." Dress up "attire elaborately" is from 1670s; dressing down "wearing clothes less formal than expected" is from 1960. To dress (someone) down (1769) is ironical. Related: Dressed;