arm-

1. A device for giving a warning of danger.
2. A security device fitted to property; especially, a house or car, to make a warning sound if a break-in or theft is attempted.
3. A reference to an "alarm clock" or "alarm watch".
4. Fear caused by the perception of imminent danger.

Historical Development

From the old French summons to battle a l'arme!, "to arms!" it seems a far cry to the modern alarm clock; yet, that is actually the scope of the word's development.

A l'arme! was first the call itself and then, in the form alarme, it became the name of this sudden summons.

The English alarm, which comes from this origin, first had the same meaning, but gradually broadened to indicate a warning signal of any kind of danger, and then the apparatus for giving this signal; such as, a fire bell.

It is interesting to also note that alarm has developed an additional meaning: the fear which results from a warning of danger.

1. The power in arms; a term originally associated with Mars, the Roman god of war.
2. Powerful in arms; mighty in battle.