chum /tʃʌm/ BrE AmE noun
[ Sense 1: Date: 1600-1700 ; Origin: Probably from chamber-fellow 'someone sharing a room' ]
[ Sense 2: Date: 1800-1900 ; Origin: Origin unknown ]
1 . [countable] informal old-fashioned a good friend:
Freddie’s an old school chum of mine.
2 . [uncountable] small pieces of oily fish, used to catch other fish