[1] : The Collaborative International Dictionary of English v.0.48

columnist \col"umnist\, n.
   a journalist who writes or edits a regularly scheduled
   column8 in a periodical, usually in editorial style; a type
   of editorialist.
   rp

   fifth columnist see fifth columnist in the vocabulary.
see also:
fifth columnist 

[2] : WordNet (r) 2.0

fifth columnist
     n : a member of a clandestine subversive organization who tries
         to help a potential invader syn: saboteur
see also:
saboteur 

[3] : Moby Thesaurus II by Grady Ward, 1.0

38 moby thesaurus words for "fifth columnist":
   trojan horse, apostate, backslider, bolter, collaborationist,
   collaborator, convert, crypto, defector, deserter, fellow traveler,
   fifth column, fraternizer, mugwump, proselyte, quisling,
   recidivist, recreant, renegade, renegado, renegate, reversionist,
   runagate, saboteur, schismatic, seceder, secessionist,
   security risk, separatist, strikebreaker, subversive, tergiversant,
   tergiversator, traitor, turnabout, turncoat, turntail,
   underground

Fifth Columnist >> F Words
Fifth Columnist, definition of term: Fifth Columnist
fifth+columnist_pag1.html

Fifth >> F Words
Fifth, definition of term: Fifth
fifth_pag1.html

Columnist >> C Words
Columnist, definition of term: Columnist
columnist_pag1.html

Fifth Wheel >> F Words
Fifth Wheel, definition of term: Fifth Wheel
fifth+wheel_pag1.html

Fifth Generatio >> F Words
Fifth Generatio, definition of term: Fifth Generatio
fifth+generatio_pag1.html

Fifth Column >> F Words
Fifth Column, definition of term: Fifth Column
fifth+column_pag1.html

Fifth Amendment >> F Words
Fifth Amendment, definition of term: Fifth Amendment
fifth+amendment_pag1.html