The Collaborative International Dictionary of English v.0.48:

Deserter \De*sert"er\ (d[-e]*z[~e]rt"[~e]r), n.
   One who forsakes a duty, a cause or a party, a friend, or any
   one to whom he owes service; especially, a soldier or a
   seaman who abandons the service without leave; one guilty of
   desertion.
   [1913 Webster]

WordNet (r) 3.0 (2006):

deserter
    n 1: a disloyal person who betrays or deserts his cause or
         religion or political party or friend etc. [syn:
         deserter, apostate, renegade, turncoat, recreant,
         ratter]
    2: a person who abandons their duty (as on a military post)
       [syn: deserter, defector]

Moby Thesaurus II by Grady Ward, 1.0:

51 Moby Thesaurus words for "deserter":
   Sabbath-breaker, absconder, apostasy, apostate, atheist,
   backslider, betrayal, blasphemer, bolt, bolter, breakaway,
   collaborationist, collaborator, convert, defection, defector,
   dereliction, desertion, escapee, fifth columnist, fugitive,
   mugwump, outlaw, proselyte, quisling, rat, ratting, recidivist,
   recreant, renegade, renegado, renegate, reversionist, runagate,
   runaway, sacrilegist, schism, schismatic, seceder, secession,
   secessionist, separatist, strikebreaker, tergiversant,
   tergiversator, traitor, turnabout, turncoat, turntail, unbeliever,
   walkout



Bouvier's Law Dictionary, Revised 6th Ed (1856):

DESERTER. One who abandons his post; as, a soldier who abandons the public
service without leave; or a sailor who abandons a ship when he has engaged
to serve.