(n.) A principal enemy. Specifically, Satan, the grand adversary of mankind.

adversative adverse alien antagonist antagonistic anti antipathetic antithetic archenemy assailant bitter enemy clashing combatant competitive competitor con conflicting contradictory contrary counter cross devil disaccordant dissentient enemy foe foeman fractious hostile inimical negative noncooperative obstinate open enemy opponent opposed opposing opposing party opposite opposite camp oppositional oppositive oppugnant overthwart perverse public enemy recalcitrant refractory repugnant rival sworn enemy the loyal opposition the opposition uncooperative unfavorable unfriendly unpropitious