early 15c., "to copulate" (of wolves, dogs), literally "to range (things) in a line," from Old French alignier "set, lay in line" (Modern French aligner), from à "to" (see ad-) + lignier "to line," from Latin lineare "reduce to a straight line," from linea (see line (n.)). Transitive or reflexive sense of "to fall into line" is from 1853. International political sense is attested from 1934. The French spelling with -g- is unetymological, and aline was an early form in English. Related: Aligned; aligning.
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.