Green’s Dictionary of Slang

1. (US black, also jello) to have sexual intercourse.

1927		T. Alexander ‘Long Lonesome Day Blues’ 🎵 Woman, you done jelly your last old time for me.
1960		P. Oliver Blues Fell this Morning 124: So a lover admires his ‘jelly bean’ and the way she can ‘jello’.

2. (US) to dance.

1939

‘Citadel Gloss.’ in AS XIV:1 Feb. 28/1: jelly, v. to dance eccentrically.

3. (US) to walk provocatively.

1949

J.H. Burns Lucifer with a Book 91: And rolling her breasts and hips, she jellied off with her husband.

4. (US street gang) to beat someone up.

1991

(con. 1982) in M. Jankowski Islands in the Street 163: We kicked ass, and I went in first and jellied a number of the [rival gang name]. [...] Man, I was like President Thatcher of England after the Falklands shit, check it out!

5. see jell v.