Green’s Dictionary of Slang

chum n.

also chummie, chummy
[17C SE chum, one who lodges in the same college rooms. Presumably f. chamber, poss. abbr. chamber-fellow or chamber-mate, although no proof has been discovered; NB ‘Sl. Terms & the Gypsy Tongue’ in Baily’s Mag. Nov. 1871 suggests origin in Rom. tschummer / Hindi chuma, a kiss ]

1. [late 17C+] (also chumbuddy) a close friend, a room-mate [mid-19C+ use is SE, although Hotten (1859) includes it since it is ‘in such frequent use with the lower orders that it demanded a place in this glossary’].

2. [late 18C–19C] (UK Und.) a fellow-prisoner.

3. [mid-19C+] (also chummy) a term of friendly address.

4. [late 19C] the vagina [i.e. the ‘friend’ of the penis].

5. [1990s+] (UK juv., also chum boy, chummer) a male homosexual.

6. see new chum n.

In compounds

chum-master (n.)

[early–mid-19C] (UK prison) an official responsible for allotting prisoners to cells, on payment of a fee.

chum-ticket (n.)

[early–mid-19C] (UK prison) a paper that on payment of a fee gives a new prisoner the right of a place in a cell.

In phrases