alarm vs foghorn

alarm and foghorn both are nouns.

Word	Noun	Adjective	Verb	Adverb
alarm	Yes	No	Yes	No
foghorn	Yes	No	No	No

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

alarm (noun)	foghorn (noun)
a device that signals the occurrence of some undesirable event	a warning device consisting of a horn that generates a loud low tone
a clock that wakes a sleeper at some preset time	a loud low warning signal that can be heard by fogbound ships
an automatic signal (usually a sound) warning of danger
fear resulting from the awareness of danger

alarm (verb)	foghorn (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