c. 1600, "a garment or assemblage of garments," originally any clothing, especially that appropriate to rank or to some ceremony; the specific sense of "woman's garment consisting of a skirt and waist" is recorded by 1630s, with overtones of "made not merely to clothe but to adorn." Dress rehearsal first recorded 1828.
c. 1300, "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 "make straight," from Latin directus "direct, straight," past participle of dirigere "set straight," from dis- "apart" (see dis-) + regere "to direct, to guide, keep straight" (from PIE root *reg- "move in a straight line").
Sense of "decorate, adorn" is from late 14c., as is that of "put on clothing." The older sense survives in military dress ranks "align columns of troops." Of males, in reference to the position of the sex organ in trousers, by 1961.
Dress up "attire elaborately, put on one's best clothing" is from 1670s; dress down "wear clothes less formal than expected" is by 1960. Transitive use of dress (someone) down, "scold, reprimand," is by 1876, earlier simply dress (1769), in which the sense is ironical. In Middle English, dress up meant "get up" and dress down meant "to kneel." Related: Dressed; dressing.
Old English hæt "hat, head covering" (variously glossing Latin pileus, galerus, mitra, tiara), from Proto-Germanic *hattuz "hood, cowl" (source also of Frisian hat, Old Norse hattr, höttr "a hood or cowl"), of uncertain etymology; it has been compared with Lithuanian kuodas "tuft or crest of a bird" and Latin cassis "helmet" (but this is said to be from Etruscan).
To throw (one's) hat in the ring was originally (1847) to take up a challenge in prize-fighting. To eat one's hat (1770), expressing what one will do if something he considers a sure thing turns out not to be, is said to have been originally eat Old Rowley's [Charles II's] hat.