mutual adjective [not gradable]
(of two or more people or groups) feeling the same emotion, or doing the same thing to or for each other
Their relationship fast degenerated into mutual recrimination(s).
Despite differences in background and outlook, their partnership was based on mutual respect, trust and understanding.
Both countries are acting to their mutual advantage.
The agreement was terminated by mutual consent.

A mutual friend is a person who is the friend of two people but in separate situations, so that the two people might not know each other.
Lynn and Phil met through a mutual friend.

Mutual fund is Am for unit trust.
See at unit (SEPARATE PART).

(saying) 'The feeling's mutual' is sometimes said after one person has expressed dislike for another.
He said, "I hate your guts" and I just said, "Well, the feeling's mutual!".

mutually adverb [not gradable]
It will be a mutually beneficial project.
Being rich and being a Socialist are not mutually exclusive (=they can exist together at the same time).