Green’s Dictionary of Slang

(orig. RN, usu. juv.) an uncircumcised penis; thus the boy/man who has one.

1959		personal recollection.
1997		Roger’s Profanisaurus in Viz 87 Dec. n.p.: cavalier n. Uncircumcised penis.
2001		OnLine Dict. of Playground Sl. 🌐 cavalier n. uncircumcised penis.
2019		P. Baker Fabulosa 290/1: Cavaliers and Roundheads uncircumcised and circumcised penises.