half track vs caterpillar tread

half track and caterpillar tread both are nouns.

Word	Noun	Adjective	Verb	Adverb
half track	Yes	No	No	No
caterpillar tread	Yes	No	No	No

As nouns, caterpillar tread is a hypernym of half track; that is, caterpillar tread is a word with a broader meaning than half track:

half track: a track that goes around only rear wheels
caterpillar tread: an endless metal belt on which tracked vehicles move over the ground

Other hypernyms of half track include caterpillar track, track.

half track (noun)	caterpillar tread (noun)
a track that goes around only rear wheels	an endless metal belt on which tracked vehicles move over the ground
a motor vehicle propelled by half tracks; frequently used by the military