someone who fights (or is fighting)
"The fighter climbed to the top of the hill, ready to engage in battle against the enemy forces."
a high-speed military or naval airplane designed to destroy enemy aircraft in the air
"The fighter broke through the clouds and intercepted the invading bomber before it could drop its payload."
A person who fights; a combatant.
"The fighter was injured during the intense battle on the front lines."
In plain English: A fighter is someone who fights hard to win an argument, competition, or battle against something difficult.
"The fighter jet took off from the runway just after dawn."
The word fighter comes from Middle English and Old English, where it originally meant a person who fights. It is formed by combining the verb fight with the suffix -er.