Unicorn

The term originated in 1970s swinger circles to describe an exceptionally rare profile: a single bisexual woman willing to play with both halves of an established heterosexual couple, equally and on the couple's terms. Wikipedia's article on unicorn hunting traces the etymology to the mythical creature's scarcity and notes the parallel slang dragon for the much rarer bisexual male equivalent. Couples who actively pursue this configuration are called unicorn hunters, and the search itself has become a recognised pattern with its own etiquette literature.

The arrangement draws sustained criticism from the polyamorous and LGBT communities, primarily for the structural couple privilege baked in: the established pair typically writes the rules, retains a unilateral veto, and treats the third partner as additive to their relationship rather than as an autonomous person with equal standing. Common couple-imposed conditions include relational exclusivity (the unicorn cannot date others), required equal attraction to both partners, no independent contact between the unicorn and either member, and group-only sex. Those terms structurally cast the unicorn as a secondary partner without negotiating power, and writers across the polyamory community routinely flag the pattern as fetishising bisexual women.

In lifestyle (rather than polyamory) contexts the term is used more loosely and often without the same political charge, since most lifestyle play is recreational rather than relational and unicorns are typically sought for single encounters rather than ongoing membership. The structural critique still applies, though, and experienced clubs and parties usually advise hunting couples to lead with respect, drop demands of equal attraction, and accept that the third partner gets veto power too.