Present participle of chum: being close friends with someone, or sharing living quarters together.
From 'chum' with the present participle suffix '-ing.' Describes the ongoing action of being or acting as a friend/roommate. The '-ing' form makes the action continuous.
In fishing, 'chumming' means throwing fish scraps in the water to attract sharks—funny that the friendliest verb in English shares its name with something that baits predators.
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