autobus vs omnibus

autobus and omnibus both are nouns.

Word	Noun	Adjective	Verb	Adverb
autobus	Yes	No	No	No
omnibus	Yes	Yes	No	No

As nouns, autobus and omnibus are synonyms defined as:

autobus and omnibus: a vehicle carrying many passengers; used for public transport

Other synonyms of autobus include bus, charabanc, coach, double-decker, jitney, motorbus, motorcoach, passenger vehicle.

autobus (noun)	omnibus (noun)
a vehicle carrying many passengers; used for public transport	a vehicle carrying many passengers; used for public transport
	an anthology of articles on a related subject or an anthology of the works of a single author

autobus (adjective)	omnibus (adjective)
	providing for many things at once