alarm vs frighten

alarm is a noun but frighten is not a noun.

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

As verbs, frighten is a hypernym of alarm; that is, frighten is a word with a broader meaning than alarm:

Other hypernyms of alarm include affright, fright, scare.

alarm (noun)	frighten (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

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