ambulance vs auto

ambulance and auto both are nouns.

Word	Noun	Adjective	Verb	Adverb
ambulance	Yes	No	No	No
auto	Yes	No	No	No

As nouns, auto is a hypernym of ambulance; that is, auto is a word with a broader meaning than ambulance:

ambulance: a vehicle that takes people to and from hospitals
auto: a motor vehicle with four wheels; usually propelled by an internal combustion engine

Other hypernyms of ambulance include automobile, car, machine, motorcar.

ambulance (noun)	auto (noun)
a vehicle that takes people to and from hospitals	a motor vehicle with four wheels; usually propelled by an internal combustion engine