interstate highway vs highway

interstate highway and highway both are nouns.

Word	Noun	Adjective	Verb	Adverb
interstate highway	Yes	No	No	No
highway	Yes	No	No	No

As nouns, highway is a hypernym of interstate highway; that is, highway is a word with a broader meaning than interstate highway:

interstate highway: one of the system of highways linking major cities in the 48 contiguous states of the United States
highway: a major road for any form of motor transport

Other hypernyms of interstate highway include main road.

interstate highway (noun)	highway (noun)
one of the system of highways linking major cities in the 48 contiguous states of the United States	a major road for any form of motor transport