Old English locere "one engaged in looking," agent noun from look (v.). Meaning "one who watches over" is from c. 1300. Sense of "one who has a certain appearance" is late 15c.; slang meaning "attractive woman" attested from 1893 (good-looker is attested from 1866, both of women and horses). Looker-on "observer, spectator" is by 1590s; looker-in (1927) was an early word for "television viewer." In Middle English a lokere-oute was "one who divines by looking at entrails."