Unicorn
A unicorn is a single person, often a bisexual woman, sought by an existing couple as a third partner for a threesome or triad relationship.
Within non-monogamy and swinger communities, "unicorn" describes a single person recruited by an already-established couple to join them for a sexual encounter, an ongoing triad relationship, or something in between. The term reflects how rare and sought-after this role is treated as being: a partner willing to join an existing couple on the couple's terms, without necessarily becoming an equal, independent partner to either person individually. Although unicorns are frequently assumed to be bisexual women recruited by heterosexual couples, the role is not limited to that configuration; couples and their sought third can be any combination of genders and orientations. "Unicorn hunting" refers to a couple actively searching for this third partner, a phrase that has taken on a negative connotation within ethical non-monogamy (ENM) communities, since it can frame the search as pursuing an object to complete the couple rather than pursuing a full, independent partner with their own needs and boundaries. The key structural distinction between a unicorn arrangement and a throuple or other polyamorous triad is hierarchy: in a unicorn arrangement, the original couple typically remains the primary, decision-making relationship, while a throuple more often treats all three people as equal partners without one pre-existing pair holding structural priority.