tertium quid

English

Etymology

Borrowed from Latin tertium quid (“third thing”).

Noun

tertium quid (plural tertium quids)

1. Something intermediate between two classifications.
2. A third party in a situation, such as one who comes between two potential romantic partners; a "gooseberry" or "third wheel".
   • 1888, Rudyard Kipling, At the Pit's Mouth:

     Once upon a time there was a Man and his Wife and a Tertium Quid.