alarm vs motor horn

alarm and motor horn both are nouns.

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

As nouns, motor horn is a hyponym of alarm; that is, motor horn is a word with a more specific, narrower meaning than alarm:

Other hyponyms of alarm include automobile horn, car horn, hooter, horn, burglar alarm, fire alarm, smoke alarm, horn, siren.

alarm (noun)	motor horn (noun)
a device that signals the occurrence of some undesirable event	a device on an automobile for making a warning noise
a clock that wakes a sleeper at some preset time
an automatic signal (usually a sound) warning of danger
fear resulting from the awareness of danger

alarm (verb)	motor horn (verb)
warn or arouse to a sense of danger or call to a state of preparedness
fill with apprehension or alarm; cause to be unpleasantly surprised