"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."
"fish bait," consisting usually of pieces of some other fish, 1857, perhaps from Scottish chum "food."