Chum
late 17th century (originally Oxford University slang, denoting a room-mate): probably short for chamber-fellow . Compare with comrade and crony.
wiktionary
1675–85; of uncertain origin, possibly from cham, shortening of chambermate, or from comrade. Less likely from Welsh cymrawd(“fellow”), compare brawd(“brother”).
Originally American English, from the 1850s. Perhaps from Powhatan.
chum (plural chums)
etymonline
chum (n.1)
"friend, intimate companion," 1680s, originally university slang for "roommate," an alternative spelling of cham, short for chamber(mate); the formation is typical of the late-17c. fondness for clipped words. Among derived forms used 19c. were chumship; chummery "shared bachelor quarters," chummage "system of quartering more than one to a room."
chum (n.2)
"fish bait," consisting usually of pieces of some other fish, 1857, perhaps from Scottish chum "food."
