in a mutual or shared manner
"the agreement was mutually satisfactory"
"the goals of the negotiators were not reciprocally exclusive"
in the same way, each to the other; reciprocally
"The two neighbors looked at each other mutually, knowing that both had made a mistake."
In plain English: Mutually means something that happens between two people who both agree to it and benefit from it together.
"They mutually agreed to end their partnership on friendly terms."
Usage: Use mutually when two parties exchange something equally or share an action together, such as agreeing on terms. Avoid confusing it with words like individually if you mean separate actions taken by one person alone.
Mutually is formed by adding the suffix -ly to the word mutual. It entered English as an adverb describing actions shared between two or more parties.