Yours, Etc.: Origins and Uses of 8 Sign-Offs
Old English locere "one engaged in looking," agent noun from look (v.). Meaning "one who watches over" is from c.1300; that of "one who has a certain appearance" is late 15c. Slang meaning "attractive woman" attested from 1893. Looker-in (1927) was an early word for "television viewer."