Green’s Dictionary of Slang

1. (US Und.) to protect a pickpocket or other sleight-of hand criminal while they work.

1885		Ledger (Noblesville, IN) 14 Aug. 6/2: ‘His partner “shaded” him and then “peached”’.
1933		Ersine Und. and Prison Sl.
1968		J. Colebrook Cross of Lassitude 101: The termites of the life [...] who ‘prat’ and ‘fan’ and ‘shade the stick’ in crowds.

2. (US) in cards, to lay down a smaller bet than one declares.

1914

T.A. Dorgan Indoor Sports 13 May [synd. cartoon] ‘They caught Little Eddie shading again’ [...] ‘Yeah — He’s as straight as a corkscrew’.

3. (US black) to hide, to conceal.

1951		D. Dressler Parole Chief 245: While taking from the inside pocket, the wire ‘shades’ the duke – conceals his hand so the victim won’t see it.
1960		‘Lord Buckley’ Hiparama of the Classics 15: They can never successfully shade what they vanced here.
1992		T. Williams Crackhouse 151: shade to conceal.
2019		D. Winslow Border [ebook] [T]hinking about fucking her, but he kept that shaded because he knew women don’t like that.

4. see throw shade under throw v.