From The Collaborative International Dictionary of English v.0.48 [gcide]:
Shammer \Sham"mer\, n.
One who shams; an impostor. --Johnson.
[1913 Webster]
From WordNet (r) 3.0 (2006) [wn]:
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]