WordNet (r) 3.0 (2006):

nonaggressive
    adj 1: not aggressive; not given to fighting or assertiveness
           [syn: unaggressive, nonaggressive] [ant:
           aggressive]

Moby Thesaurus II by Grady Ward, 1.0:

43 Moby Thesaurus words for "nonaggressive":
   bone-lazy, cadging, civilian, conciliatory, dilatory, do-nothing,
   doless, dovish, dronish, drony, easy, ergophobic, faineant,
   good-for-nothing, indolent, irenic, laggard, lax, lazy,
   noncombatant, nonmilitant, nonviolent, pacific, pacifist,
   pacifistic, parasitic, peace-loving, peaceable, procrastinative,
   remiss, scrounging, shiftless, slack, slothful, slow, sponging,
   unbellicose, uncontentious, unenterprising, unhostile, unmilitant,
   unmilitary, work-shy