charabanc vs school bus

charabanc and school bus both are nouns.

Word	Noun	Adjective	Verb	Adverb
charabanc	Yes	No	No	No
school bus	Yes	No	No	No

As nouns, school bus is a hyponym of charabanc; that is, school bus is a word with a more specific, narrower meaning than charabanc:

Other hyponyms of charabanc include minibus, trackless trolley, trolley coach, trolleybus.

charabanc (noun)	school bus (noun)
a vehicle carrying many passengers; used for public transport	a bus used to transport children to or from school