motor horn vs car horn

motor horn and car horn both are nouns.

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

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

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

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

motor horn (noun)	car horn (noun)
a device on an automobile for making a warning noise	a device on an automobile for making a warning noise