Learner's definition of LOSER
someone or something that loses a game, contest, etc.
She was a loser in the first round of the tournament. [=she lost in the first round of the tournament]
The team had a reputation for being a loser year after year.
The loser of the bet has to buy drinks for the winner.
She's a good loser. [=she does not become upset or angry when she loses]
He's a bad/poor loser. = (US) He's a sore loser. [=he becomes upset or angry when he loses]
someone who is harmed or put in a worse position as the result of something
informal + disapproving
a person who is not successful, attractive, etc.
finders keepers (losers weepers)