Green’s Dictionary of Slang

broth n.

[abbr.]

(US campus) brother.

[UK]A. Burgess Right to an Answer (1978) 39: She said to me, "Well, broth [...] it’s ready’.
[US]Eble Campus Sl. Mar. 1: broth – brother.
[US]Eble Sl. and Sociability 36: All types of shortening are evident in college slang. The most frequent pattern of clipping is the loss of sounds from the ends of words: [...] bro and broth, from brother.

In compounds