0 to feel that you belong to a particular group and are accepted by that group: --
1 to belong with other things, or to be accepted by other people in a group: --
2 to feel you belong to a particular group and are accepted by the other members: --
3 to be suitable or right in a particular situation: --
Being the only father at the mothers-and-toddlers group, he struggled to fit in at first.
I tried so hard to fit in, but the other staff there were reluctant to accept me.
It became clear very quickly that the new assistant wasn't going to fit in.
She's exactly the type of person we need in our department - she should fit in perfectly.