venki

The object of venki is whoever or whatever you beat: an enemy, an army, your own fear. That is the difference from gajni, whose object is what you carry off - a prize, money, a match. So you venkas la kontraŭulon and gajnas la ludon, and mixing them up is the commonest slip here. Venko is a victory, venkinto the winner, nevenkebla invincible, and malvenki is to lose in the sense of being beaten, which is not the same as perdi, losing your keys.