The Collaborative International Dictionary of English v.0.48:

Shirker \Shirk"er\, n.
   One who shirks. --Macaulay.
   [1913 Webster]

WordNet (r) 3.0 (2006):

shirker
    n 1: a person who shirks his work or duty (especially one who
         tries to evade military service in wartime) [syn:
         slacker, shirker]

Moby Thesaurus II by Grady Ward, 1.0:

29 Moby Thesaurus words for "shirker":
   bungler, clock watcher, disregarder, dodger, eye-servant,
   goldbrick, goldbricker, goof-off, idler, ignorer, malingerer,
   neglecter, negligent, old soldier, procrastinator, shirk, skulk,
   skulker, slacker, slinker, sloven, slut, soldier, spiv, tax dodger,
   trifler, truant, waiter on Providence, welsher