trolleybus vs double-decker

trolleybus and double-decker both are nouns.

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

As nouns, double-decker is a hypernym of trolleybus; that is, double-decker is a word with a broader meaning than trolleybus:

trolleybus: a passenger bus with an electric motor that draws power from overhead wires
double-decker: a vehicle carrying many passengers; used for public transport

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

trolleybus (noun)	double-decker (noun)
a passenger bus with an electric motor that draws power from overhead wires	a vehicle carrying many passengers; used for public transport