Green’s Dictionary of Slang

the female breasts.

a.1790		C. Dibdin ‘Buxom Nan’ in Collection of Songs II 72: Tant masted all, to see who’s tallest, / Breastworks, top gant-sails, and a fan; / Mesmate, cried I, more sail than ballast, / Ah still give me my buxom Nan.
1826		C.M. Westmacott Eng. Spy II 368: The frigate yonder with the brown breast works, and she with the pink facings, look something like privateers.
1873		F.W. Benteen in letter 31 July Carroll Camp Talk (1983) 9: I am intrenched behind breastworks of logs—which are well ditched—and really formidable. I know of breastworks that I would prefer being before tho’.
1926		‘lydia pinkham’ song in Canfield Coll. Oh, Mrs Smith—she had no breast-works / Which made her husband raise a row; / So she drank, she drank, she drank two bottles of compound, / And now they milk her like a cow!
1935		J. Conroy World to Win 156: Did you lamp them breastworks? Oi! Oi!
1946		H.A. Smith Rhubarb 93: Harold Harper, the newspaperman who forged a career by charging across the breastworks of a nation.
1950		J.T. Farrell ‘Milly and the Porker’ in Amer. Dream Girl (1950) 196: He told himself that if she bent over near his table he could see her breastworks.
1961		G.L. Coon Meanwhile, Back at the Front (1962) 180: Overshadowed by breastworks of such magnitude and design as to stagger credulity.