Source : Webster's Revised Unabridged Dictionary (1913)

Decampment \De*camp"ment\, n. [Cf. F. d['e]campement.]
   Departure from a camp; a marching off.

Source : WordNet®

decampment
     n 1: the act of running away secretly (as to avoid arrest) [syn:
          {abscondment}]
     2: breaking camp