car horn vs alarm

car horn and alarm both are nouns.

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

As nouns, alarm is a hypernym of car horn; that is, alarm is a word with a broader meaning than car horn:

Other hypernyms of car horn include alarm system, warning device.

car horn (noun)	alarm (noun)
a device on an automobile for making a warning noise	a device that signals the occurrence of some undesirable event
	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

car horn (verb)	alarm (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