Definition of "compersion"

A major component of jealousy, for many people, is the suspicion or resentment of the rival. In Kerista, on the other hand, the relationship that every man had with the other men and that every woman had with the other women elicited what they called “compersion” rather than jealousy.

1998, Ayala Malach Pines, Romantic Jealousy: Causes, Symptoms, Cures, Routledge, page 140

There is nothing either magical or wrong with sex with more than one person at the same time. […] The beautiful thing about this dynamic is that it offers opportunities for compersion (the opposite of jealousy) and is symbolic of the expansiveness and unity we can feel in our love for each other.

2003, Mystic Life, Spiritual Polyamory, iUniverse, page 46

I think this is the easiest way to teach compersion, to immerse oneself in the unconditional approval of another person’s pleasure.We usually seek compersion in the context of our lover being sexual with another person, which can be very beautiful, but equally scary.Compersion is the coveted secret elixer of emotions because it promises to turn the pain of jealousy into an ecstatic calm, or ecstatic release.

2005, Serena Anderlini-D’Onofrio, editor, Plural Loves, Haworth Press, page 174

Some polyamorous people experience compersion, which means feeling joy that one’s partner is sharing closeness with another person (Keener, 2004; Polyamory Society, 1997). Keener’s (2004) study participants noted an absence of worry as to whether their partners might be cheating […]

2006, Ronald C. Fox, Ph.D. (editor), Affirmative Psychotherapy with Bisexual Women and Bisexual Men, Haworth Press, page 140