Other forms: disarmed, disarming, disarms
To disarm is to take weapons away. Disarm the suspect, disarm the militia, nuclear disarmament.
It also means to make a device safe: disarm the bomb, disarm the alarm. The figurative sense is to win somebody over so completely that they stop being hostile: a disarming smile, disarmed by her honesty — and disarming is much the commoner form. Note disarmament, which in international politics means agreed reduction of weapons; and unilateral disarmament, meaning doing it without waiting for anybody else.
1verbdisarmTo take weapons away, or to make a device safe.
“Army experts were called in to disarm the bomb.”
2verbwinTo win somebody over so they stop being hostile.
“Her warm smile disarmed the angry customer.”
disarm is a removing of weapons or hostility.
Old French desarmer is des-, undoing, plus armer, to arm, from Latin arma, weapons. The figurative sense is the same idea: somebody disarming has removed your reasons for fighting.
Anglo-Norman
desarmer
Middle English
desarmen — to divest of arms
English, today
disarm
From Middle English desarmen (“to divest of arms”), from Anglo-Norman desarmer.
Etymology from Wiktionary, CC BY-SA