A person who habitually gets into fights or is known for brawling; often carries a rough, streetwise connotation.
That man is a well-known brawler in town.
When he was young, he was feared as a ruffian.
Compound of 喧嘩 (けんか, 'fight, quarrel') and 師 (し, 'master, specialist'), literally 'fight master'. The exact historical derivation is uncertain, but it follows a common pattern for describing a person known for a particular behavior.