Top Definition
An intimate friend; a really kindred spirit to whom you can confide your inmost soul. Very hard to find.
1) I'm so glad I met Lin. She is a bosom friend!

2) I never expected to find such a bosom friend, but I'm glad I did.
by Can't you guess who I am??? June 13, 2010
A very close friend. One that you can share everything with. Made popular by Anne in Anne of Green Gables.
Anne: "Diana Barry is my bosom friend"
by TheRealIndianaJones January 02, 2016
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