Source : Webster's Revised Unabridged Dictionary (1913)

Loser \Los"er\, n.
   One who loses. --South.

Source : WordNet®

loser
     n 1: a contestant who loses the contest [syn: {also-ran}] [ant: {winner}]
     2: a person with a record of failing; someone who loses
        consistently [syn: {failure}, {nonstarter}, {unsuccessful
        person}] [ant: {achiever}]
     3: a gambler who loses a bet [ant: {winner}]

Source : Free On-Line Dictionary of Computing

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)