fighter vs warplane

fighter and warplane both are nouns.

Word	Noun	Adjective	Verb	Adverb
fighter	Yes	No	No	No
warplane	Yes	No	No	No

As nouns, warplane is a hypernym of fighter; that is, warplane is a word with a broader meaning than fighter:

fighter: a high-speed military or naval airplane designed to destroy enemy aircraft in the air
warplane: an aircraft designed and used for combat

Other hypernyms of fighter include aeroplane, airplane, plane, military plane.

fighter (noun)	warplane (noun)
a high-speed military or naval airplane designed to destroy enemy aircraft in the air	an aircraft designed and used for combat
someone who fights (or is fighting)
someone who fights for a cause