1 warfare, combat, conflict, fighting, clash, hostilities, battle, struggle, engagement, encounter, strife, contention:
The war, in which several millions died, lasted six years.
2 at war. fighting, battling, in combat, in conflict; in disagreement, in dispute, in contention, struggling, antagonistic, at daggers drawn:
They are at war because an ambassador refused to retract some silly insult.
3 do battle or fight or struggle or (engage in) combat with or against, make or wage war with or against, take up arms or strive or campaign or tilt against, cross swords or contend or joust with:
We must continue to war against the forces of evil.