The Collaborative International Dictionary of English v.0.48:

Shammer \Sham"mer\, n.
   One who shams; an impostor. --Johnson.
   [1913 Webster]

WordNet (r) 3.0 (2006):

shammer
    n 1: someone shirking their duty by feigning illness or
         incapacity [syn: malingerer, skulker, shammer]
    2: a person who makes deceitful pretenses [syn: imposter,
       impostor, pretender, fake, faker, fraud, sham,
       shammer, pseudo, pseud, role player]