frighten vs alarm

frighten is not a noun while alarm is a noun.

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

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

frighten (noun)	alarm (noun)
	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

frighten (verb)	alarm (verb)
cause fear in	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