Green’s Dictionary of Slang

crook n.1

1. a finger.

[UK]G. Parker Life’s Painter 167: Fingers. Crooks.

2. (US black/Harlem) an elbow.

[US]D. Burley Orig. Hbk of Harlem Jive 12: I’m stiffing the stroll on the flag spot when up pops a fine banana with a cluck stud hanging on her crook.