Latin adjective, "unconquered, unsubdued, invincible," from in- "not, opposite of" (see in- (1)) + victus, past participle of vincere "to conquer, overcome" (from nasalized form of PIE root *weik- (3) "to fight, conquer").
It matters not how strait the gate,
How charged with punishments the scroll,
I am the master of my fate,
I am the captain of my soul.
[William Ernest Henley, "Invictus"]