The Collaborative International Dictionary of English v.0.48:

Enlistment \En*list"ment\, n.
   1. The act or enlisting, or the state of being enlisted;
      voluntary enrollment to serve as a soldier or a sailor.
      [1913 Webster]

   2. The writing by which an enlisted man is bound.
      [1913 Webster]

WordNet (r) 3.0 (2006):

enlistment
    n 1: a period of time spent in military service [syn:
         enlistment, hitch, term of enlistment, tour of
         duty, duty tour, tour]
    2: the act of enlisting (as in a military service)