alarum vs air alert

alarum and air alert both are nouns.

Word	Noun	Adjective	Verb	Adverb
alarum	Yes	No	No	No
air alert	Yes	No	No	No

As nouns, air alert is a hyponym of alarum; that is, air alert is a word with a more specific, narrower meaning than alarum:

alarum: an automatic signal (usually a sound) warning of danger
air alert: the warning signal that begins a period of preparation for an enemy air attack

Other hyponyms of alarum include torpedo, burglar alarm, fire alarm, foghorn, fogsignal, horn, red flag, siren, alarm bell, tocsin.

alarum (noun)	air alert (noun)
an automatic signal (usually a sound) warning of danger	the warning signal that begins a period of preparation for an enemy air attack
	the condition in which combat aircraft are airborne and ready for an operation
	the time period during which military and civilian agencies are prepared for an enemy air attack