alarm:  Alarm was originally a call to arms. It comes from the Old Italian phrase all’ arme ‘to the weapons!’ This was lexicalized as the noun allarme, which was borrowed into Old French as alarme, and thence into English. The archaic variant alarum seems to have arisen from an emphatic rolling of the r accompanying a prolongation of the final syllable when the word was used as an exclamation. => arm
early 14c., from Old French alarme (14c.), from Italian all'arme "to arms!" (literally "to the arms"). An interjection that came to be used as the word for the call or warning (compare alert). Extended 16c. to "any sound to warn of danger or to arouse." Weakened sense of "apprehension, unease" is from 1833. Variant alarum is due to the rolling -r- in the vocalized form. Sometimes in early years anglicized as all-arm. Alarm clock is attested from 1690s (as A Larum clock).