fighter vs military plane

fighter and military plane both are nouns.

Word	Noun	Adjective	Verb	Adverb
fighter	Yes	No	No	No
military plane	Yes	No	No	No

As nouns, military plane is a hypernym of fighter; that is, military plane 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
military plane: an aircraft designed and used for combat

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

fighter (noun)	military plane (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