A Supernumrary

1. A person who works in a group, association, or public office without forming part of the regular staff (the numerary). [from early 17th c.]
2. (film, theater) An extra or walk-on, often non-speaking, in a film or play; a spear carrier. Synonyms: supe, super
3. Something which is beyond the prescribed or standard amount or number.
4. (zoology) An animal which has not formed a pair bond and is therefore single.
5. (Roman Catholicism) A married man or woman who is a secular member of Opus Dei, a Roman Catholic religious institution.