"qualified or trained to fight," mid-14c., present-participle adjective from fight (v.). Fighting chance is from 1877; fighting mad is attested by 1750; fighting words is by 1882. Fighty "pugnacious" is attested from c. 1200.
early 13c., "act of engaging in combat," verbal noun from fight (v.). Old English had feohtlac (n.) "fighting, battle." Nautical fighting-top "platform near the top of a mast for small-arms fire" is from 1890.