late 14c., babi, dim. of baban (see babe). The verb meaning "to treat like a baby" is from 1742. As a term of endearment for one's lover it is attested perhaps as early as 1839, certainly by 1901; its popularity perhaps boosted by baby vamp "a popular girl," student slang from c.1922. Baby blues for "blue eyes" recorded by 1944 (the phrase also was used for "postpartum depression" 1950s-60s). To empty the baby out with the bath (water) is first recorded 1909 in G.B. Shaw (cf. Ger. das Kind mit dem Bade ausschütten).