The Collaborative International Dictionary of English v.0.48:

Desertion \De*ser"tion\ (d[-e]*z[~e]r"sh[u^]n), n. [L. desertio:
   cf. F. d['e]sertion.]
   1. The act of deserting or forsaking; abandonment of a
      service, a cause, a party, a friend, or any post of duty;
      the quitting of one's duties willfully and without right;
      esp., an absconding from military or naval service.
      [1913 Webster]

            Such a resignation would have seemed to his superior
            a desertion or a reproach.            --Bancroft.
      [1913 Webster]

   2. The state of being forsaken; desolation; as, the king in
      his desertion.
      [1913 Webster]

   3. Abandonment by God; spiritual despondency.
      [1913 Webster]

            The spiritual agonies of a soul under desertion.
                                                  --South.
      [1913 Webster]

WordNet (r) 3.0 (2006):

desertion
    n 1: withdrawing support or help despite allegiance or
         responsibility; "his abandonment of his wife and children
         left them penniless" [syn: desertion, abandonment,
         defection]
    2: the act of giving something up [syn: abandonment,
       forsaking, desertion]