Idioms with the word "Fifth"
1. Plead/take the fifth: Said humorously in response to a request for provocative information when one does not want to reveal it.
2. Third/fifth wheel: a person thought to be unwelcome in the company of a pair or quartet of people; usually a reference to a single person with one or two couples.
3. Fifth column: collaborators supporting would-be invaders from within a country.