The Collaborative International Dictionary of English v.0.48:
Decampment \De*camp"ment\, n. [Cf. F. d['e]campement.] Departure from a camp; a marching off. [1913 Webster]WordNet (r) 3.0 (2006):
decampment n 1: the act of running away secretly (as to avoid arrest) [syn: abscondment, decampment] 2: breaking camp