Green’s Dictionary of Slang

the female breasts, the chest; occas. in sing.

1748		Spy on Mother Midnight II 32: Our Grandmothers would not show as much of their Bosoms as you do for the World; they huddled up their Diddies in huge Ruffs and Tippets, and show’d nothing of their Faces but the Chin.
c.1786		Grose Classical Dict. of the Vulgar Tongue ms. additions n.p.: Diddys a Womans Breasts or Bubbies.
1788, 1796		Grose Classical Dict. of the Vulgar Tongue (2nd, 3rd edn) n.p.: Diddeys. A woman’s breasts or bubbies.
1811		Lex. Balatronicum.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.
1910		P.W. Joyce Eng. As We Speak It In Ireland (1979) 247: A baby sucks its mother’s diddy.
1922		Joyce Ulysses 581: Chews cocoa all day long, the communicative tarpaulin added. Stomachs like breadgraters. Cuts off their diddies when they can’t bear any more children.
1939		(con. 1880–90s) S. O’Casey I Knock at the Door 55: We met two lovely big-diddied rides, and they were all for us going home with them.
1942		(con. 1890s) S. O’Casey Pictures in the Hallway 237: An’ furry flounces round our necks as well, said the vanman, to keep our diddies warm.
1964		P. White Burnt Ones 298: He felt her warmth, her firm diddies pressed against his back.
1966		(con. 1958) R. Farina Been Down So Long (1972) 27: ‘Siamese twins? Really?’ ‘Joined at the left diddly.’.
1966		P. Boyle At Night All Cats Are Grey 73: Thrapple jigging like a step-dancer’s diddies.
1973		H. Leonard Da (1981) Act II: Bolicky Biddy had only one diddy / To feed the baby on.
1981		(con. 1920s) P. Crosbie Your Dinner’s Poured Out! 220: diddy breast.
1991		B. Quinn Smokey Hollow 41: Babies dangling from their diddies.
2001		G. Coughlan Everyday Eng. and Sl. 🌐 Diddies (n): breasts.