[syn: failure, loser, nonstarter, unsuccessful person]
3.  a gambler who loses a bet; 
The Collaborative International Dictionary of English v.0.48:
Loser \Los"er\, n.
   1. One who loses; as, the loser pays for a round of beer.
      --South.
      [1913 Webster]
   2. A person who is habitually unsuccessful at some endeavor,
      such as employment or personal relationships. [slang]
      [PJC]
   3. A plan or strategy unlikely to succeed. [slang]
      [PJC]
WordNet (r) 3.0 (2006):
loser
    n 1: a contestant who loses the contest [syn: loser, also-
         ran] [ant: victor, winner]
    2: a person with a record of failing; someone who loses
       consistently [syn: failure, loser, nonstarter,
       unsuccessful person] [ant: achiever, succeeder,
       success, winner]
    3: a gambler who loses a bet [ant: winner]
Moby Thesaurus II by Grady Ward, 1.0:
38 Moby Thesaurus words for "loser":
   also-ran, bankrupt, bomb, booby, bummer, bust, clinker, con,
   defeatee, duck, dud, failure, fall guy, false alarm, fiasco, flop,
   game loser, good loser, good sport, hard-luck guy, hardcase,
   jailbird, lag, lemon, misfit, nebbish, poor unfortunate, sad sack,
   schlemiel, schlimazel, sport, stooge, sure loser, the vanquished,
   underdog, unfortunate, victim, washout
The Jargon File (version 4.4.7, 29 Dec 2003):
loser
 n.
    An unexpectedly bad situation, program, programmer, or person. Someone who
    habitually loses. (Even winners can lose occasionally.) Someone who knows
    not and knows not that he knows not. Emphatic forms are real loser, total
    loser, and complete loser (but not **moby loser, which would be a
    contradiction in terms). See luser.
The Free On-line Dictionary of Computing (30 December 2018):
loser
    An unexpectedly bad situation, program, programmer,
   or person.  Someone who habitually loses.  (Even winners can
   lose occasionally).  Someone who knows not and knows not that
   he knows not.  Emphatic forms are "real loser", "total loser",
   and "complete loser" (but not **"moby loser", which would be a
   contradiction in terms).
   See luser.
   [Jargon File]
   (1995-04-19)