alarm clock vs alarm

alarm clock and alarm both are nouns.

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

As nouns, alarm clock and alarm are synonyms defined as:

alarm clock (noun)	alarm (noun)
a clock that wakes a sleeper at some preset time	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 clock (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