coach vs school bus

coach and school bus both are nouns.

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

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

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

coach (noun)	school bus (noun)
a carriage pulled by four horses with one driver	a bus used to transport children to or from school
a railcar where passengers ride
a vehicle carrying many passengers; used for public transport
a person who gives private instruction (as in singing, acting, etc.)
(sports) someone in charge of training an athlete or a team

coach (verb)	school bus (verb)
teach and supervise (someone); act as a trainer or coach (to), as in sports
drive or operate a coach or carriage