non-aggression n.

a prefix used freely in English and meaning "not, lack of," or "sham," giving a negative sense to any word, 14c., from Anglo-French noun-, from Old French non-, from Latin non "not, by no means, not at all, not a," from Old Latin noenum "not one" (*ne oinom, from PIE root *ne- "not" + PIE root *oi-no- "one, unique"). In some cases perhaps from Middle English non "not" (adj.), from Old English nan (see not). "It differs from un- in that it denotes mere negation or absence of the thing or quality, while un- often denotes the opposite of the thing or quality" [Century Dictionary].

1610s, "unprovoked attack," from French aggression (16c., Modern French agression), from Latin aggressionem (nominative aggressio) "a going to, an attack," noun of action from past-participle stem of aggredi "to approach; to attempt; to attack," from ad "to" (see ad-) + gradi (past participle gressus) "to step," from gradus "a step," figuratively "a step toward something, an approach" (from PIE root *ghredh- "to walk, go"). The psychological sense of "hostile or destructive behavior" is recorded by 1912 in A.A. Brill's translation of Freud.