bubby (n.)

"breasts," 1929, U.S. slang, probably from much older term boobies (late 17c.), related to 17c. bubby; all perhaps ultimately from Latin pupa, literally "little girl," hence, in child-talk, "breast." Or else it is a natural formation in English (compare French poupe "teat," German dialectal Bubbi, etc.).

"a woman's breast," 1860, short for bubby.