dual carriageway vs main road

dual carriageway and main road both are nouns.

Word	Noun	Adjective	Verb	Adverb
dual carriageway	Yes	No	No	No
main road	Yes	No	No	No

As nouns, main road is a hypernym of dual carriageway; that is, main road is a word with a broader meaning than dual carriageway:

dual carriageway: a highway divided down the middle by a barrier that separates traffic going in different directions
main road: a major road for any form of motor transport

Other hypernyms of dual carriageway include highway.

dual carriageway (noun)	main road (noun)
a highway divided down the middle by a barrier that separates traffic going in different directions	a major road for any form of motor transport