army tank vs military vehicle

army tank and military vehicle both are nouns.

Word	Noun	Adjective	Verb	Adverb
army tank	Yes	No	No	No
military vehicle	Yes	No	No	No

As nouns, military vehicle is a hypernym of army tank; that is, military vehicle is a word with a broader meaning than army tank:

army tank: an enclosed armored military vehicle; has a cannon and moves on caterpillar treads
military vehicle: vehicle used by the armed forces

Other hypernyms of army tank include armored vehicle, armoured vehicle, tracked vehicle.

army tank (noun)	military vehicle (noun)
an enclosed armored military vehicle; has a cannon and moves on caterpillar treads	vehicle used by the armed forces