car horn vs hooter

car horn and hooter both are nouns.

Word	Noun	Adjective	Verb	Adverb
car horn	Yes	No	No	No
hooter	Yes	No	No	No

As nouns, car horn and hooter are synonyms defined as:

car horn and hooter: a device on an automobile for making a warning noise

Other synonyms of car horn include automobile horn, horn, motor horn.

car horn (noun)	hooter (noun)
a device on an automobile for making a warning noise	nocturnal bird of prey with hawk-like beak and claws and large head with front-facing eyes
	a device on an automobile for making a warning noise
	informal terms for the nose