The Greek machia (battle) with the negating prefix. Literally, without battle or fighting; met. said of a person that no one wants to or can fight, thus, invincible, unconquerable, etc., or when said of places, impregnable. For this sense, cf. aprosmachic and dysmachic.
Can also mean simply one who hasn't participated in a battle, or one who won't, and thus can be used to mean peaceful. A conscientious objector to war, for instance, could be said to be amachic in the second sense. For this sense, cf. phygomachic.