Green’s Dictionary of Slang

see under giblets n.

1. (US tramp) for two or more tramps to become companions on the road; to be hired.

1921

P. & T. Casey Gay-cat 303: Join Out — to be hired by or join with someone on the road.

2. (US Und.) to join a criminal gang.

1912		A.H. Lewis Apaches of N.Y. 39: Spanish [...] had joined out with a mob [of pickpockets].
1914		Amer. Mag. 77 June 31–5: My rebuff sent me flying back to my layout and thiefdom, never to return. I ‘joined out’ with a mob and we prospered financially.

to have sexual intercourse.

1656

Muses Recr. (Hotten) 48: My Father and Mother when first they join’d paunches [F&H].

see under bird n.¹

to become a professional thief.

a.1889

‘Johnny’s Joined the Gang’ [ballad] Sure my heart is broke and mistake, / Since Johnny’s joined the gang.

(Aus.) of a prostitute, to associate herself with a pimp.

1996

(con. 1964-65) B. Thorpe Sex and Thugs and Rock ’n’ Roll 135: ‘I worked on me own and ’e kept leanin’ on me to join up’.