lucy locket, n. — Green’s Dictionary of Slang

lucy locket n.

also locket

[rhy. sl. underpinned by nursery rhyme ‘Lucy Locket lost her pocket’ recorded 1842 and prob. known earlier]

a pocket.

1935		Thieves Slang ms list from District Police Training Centre, Ryton-on-Dunsmore, Warwicks 6: Lucy Locket: Pocket.
1941		Baker Popular Dict. Aus. Sl. 44: LOCKET: A pocket. Rhyming slang.
1969		S.T. Kendall Up the Frog.
1971		J. Jones Rhy. Cockney Sl.
1981		P. Wright Cockney Dialect and Sl. 106: Lucy Locket ‘pocket’.
1992		R. Puxley Cockney Rabbit.