'fifth columnist' definitions:

Definition of 'fifth columnist'

From: WordNet
noun
A member of a clandestine subversive organization who tries to help a potential invader [syn: fifth columnist, saboteur]

Definition of 'fifth columnist'

From: GCIDE
  • columnist \col"um*nist\, n. a journalist who writes or edits a regularly scheduled column[8] in a periodical, usually in editorial style; a type of editorialist. [RP]
  • fifth columnist see fifth columnist in the vocabulary.