autobus vs double-decker

autobus and double-decker both are nouns.

Word	Noun	Adjective	Verb	Adverb
autobus	Yes	No	No	No
double-decker	Yes	No	No	No

As nouns, autobus and double-decker are synonyms defined as:

autobus and double-decker: a vehicle carrying many passengers; used for public transport

Other synonyms of autobus include bus, charabanc, coach, jitney, motorbus, motorcoach, omnibus, passenger vehicle.

autobus (noun)	double-decker (noun)
a vehicle carrying many passengers; used for public transport	a vehicle carrying many passengers; used for public transport