motor horn vs automobile horn

motor horn and automobile horn both are nouns.

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

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

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

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

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