taxi vs auto

taxi and auto both are nouns.

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

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

taxi: a car driven by a person whose job is to take passengers where they want to go in exchange for money
auto: a motor vehicle with four wheels; usually propelled by an internal combustion engine

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

taxi (noun)	auto (noun)
a car driven by a person whose job is to take passengers where they want to go in exchange for money	a motor vehicle with four wheels; usually propelled by an internal combustion engine

taxi (verb)	auto (verb)
ride in a taxicab
travel slowly