alarm vs car horn

alarm and car horn both are nouns.

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

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

alarm (noun)	car 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)	car 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