One who fights; a combatant; a warrior.
A military aircraft designed to seek out and destroy enemy aircraft; it is usually smaller and more maneuvarable than aircraft designed specifically for bombing. However, hybrid fighter-bomber aircraft that perform both functions also are used.
A ship manned by one sentient being or artificial intelligence or remotely piloted at distances where latency is not an issue. Fighters move very fast, dodging enemy missiles and energy weapons and maneuvering in close to execute quick slashing attacks before fleeing out of range. Fighters are also used to fly combat patrol in defense of Heavy Cruisers or other high-value assets.
A fighter, in this context, is a person whose career is fighting. In most systems it is a character class.