The Collaborative International Dictionary of English v.0.48:

Malingerer \Ma*lin"ger*er\, n. [F. malingre sickly, weakly,
   prob. from mal ill + OF. heingre, haingre, thin, lean,
   infirm, fr. L. aeger.]
   In the army, a soldier who feigns himself sick, or who
   induces or protracts an illness, in order to avoid doing his
   duty; hence, in general, one who shirks his duty by
   pretending illness or inability.
   [1913 Webster]

WordNet (r) 3.0 (2006):

malingerer
    n 1: someone shirking their duty by feigning illness or
         incapacity [syn: malingerer, skulker, shammer]