仲間:なかま: friendship, as in "This event affected our friendship." "Our friendship grows by the week."

But, it also means 'in the same group' (snake is `nakama' with iguana because they are both reptiles. Everyone at the bank is 'nakama' regardless of if they like each other.)

仲良し:なかよし: a good friend.

友達:ともだち: friend (casual situation)

友人:ゆうじん: friend (slightly less casual)