WAR

noun

1. Organized, large-scale, armed conflict between countries or between national, ethnic, or other sizeable groups, usually involving the engagement of military forces.
2. A particular conflict of this kind.
3. (by extension) Any conflict, or anything resembling a conflict.

verb

1. To engage in conflict (may be followed by "with" to specify the foe).
2. To carry on, as a contest; to wage.