fifth columnist vs saboteur

fifth columnist and saboteur both are nouns.

Word	Noun	Adjective	Verb	Adverb
fifth columnist	Yes	No	No	No
saboteur	Yes	No	No	No

As nouns, fifth columnist and saboteur are synonyms defined as:

fifth columnist and saboteur: a member of a clandestine subversive organization who tries to help a potential invader

fifth columnist (noun)	saboteur (noun)
a member of a clandestine subversive organization who tries to help a potential invader	someone who commits sabotage or deliberately causes wrecks
	a member of a clandestine subversive organization who tries to help a potential invader