Same word as oppositional:

adversarial, adverse, against the grain, allergic, antagonistic, anti, antipathetic, antithetical, antonymous, at cross-purposes, at odds, averse, battling, clashing, combating, conflicting, confronting, contrary, controverting, counter, crossing, defending, defensive, denying, disagreeing, disputed, disputing, dissentient, enemy, exposing, facing, gainsaying, hostile, in opposition, incompatible, inimical, irreconcilable, objecting, obstructive, opposed, opposite, protesting, repelling, restrictive, rival, up against, warring