Green’s Dictionary of Slang

a coat or a waistcoat.

1821		D. Haggart Autobiog. 25: The screaves were in his benjy cloy.
1826		Vulgarities of Speech Corrected.
1859		Hotten Dict. of Modern Sl. etc. 5: BENJY, a waistocat.
1864, 1867, 1870		Hotten Sl. Dict. [as cit. 1859].
1873		Sl. Dict.
1896		A. Morrison Child of the Jago (1982) 128: They were flimped of their kicksies, benjies, or daisies, as the case might be.