motorway vs superhighway

motorway and superhighway both are nouns.

Word	Noun	Adjective	Verb	Adverb
motorway	Yes	No	No	No
superhighway	Yes	No	No	No

As nouns, motorway and superhighway are synonyms defined as:

motorway and superhighway: a broad highway designed for high-speed traffic

Other synonyms of motorway include expressway, freeway, pike, state highway, throughway, thruway.

motorway (noun)	superhighway (noun)
a broad highway designed for high-speed traffic	a broad highway designed for high-speed traffic
	an extensive electronic network (such as the internet) used for the rapid transfer of sound and video and graphics in digital form