The Collaborative International Dictionary
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.
fifth columnist see fifth columnist in the vocabulary.
Wiktionary
n. someone who belongs to a group that secretly undermines another organization
WordNet
n. a member of a clandestine subversive organization who tries to help a potential invader [syn: saboteur]
Usage examples of "fifth columnist".
He knew well enough that no plea for mercy would have any effect, but if he said that he spoke German, had understood Grauber's remarks that the Blitzkrieg was being launched at that moment and that he was a German Fifth Columnist who had work to do for Germany, there was just a possibility that Grauber might have let him go.
That Zone Green was being penetrated by renegades was certain-but it is hard to tell a fifth columnist from a custard head.
Kenneth had wondered if Mr Robb was secretly a fifth columnist or even a Nazi, and was hiding men washed up from a sunken U-boat, or preparing a place for paratroopers to land, but despite him and some of the other children watching Mr Robb very carefully from the woods a few times, they had never been able to prove anything.
Also that Besi John, a notorious criminal and Fifth Columnist, was here on shady business.
After the start of World War n, rumors began to circulate of occult rituals, which may or may not have been a cover for Fifth Columnist activities.