1. One's close or closest friend; a friend one holds dear to one's heart. We grew up right next door to each other, so we have been bosom chums since we were kids.
2. Lice on one's body. Ugh, I'm so itchy—I really hope my bosom chums aren't back.
bosom chumsand bosom friends
n. lice. The old guy sat there scratching at his bosom chums. My bosom friends keep me awake all night.