The adjective amicable means "friendly" — but in particular, use it when describing relations one might otherwise expect to be unfriendly. The end of a romantic relationship that's less than amicable might involve broken dishes or broken bones.
Amicable, not surprisingly, comes from the Latin word for "friend," amicus. Perhaps the things most commonly described as amicable are divorces. The parties in a divorce often tend to be so childish and the proceedings so messy that it's nice to have a word that reflects the absence of those qualities. Other nouns that commonly pair with amicable include relationship, split, parting, solution, and breakup.