WordNet (r) 3.0 (2006):

muster out
    v 1: release from military service [syn: discharge, muster
         out] [ant: draft, enlist, muster in]

Moby Thesaurus II by Grady Ward, 1.0:

21 Moby Thesaurus words for "muster out":
   break up, deactivate, debrief, demob, demobilize, detach, disband,
   discharge, disintegrate, dismiss, disorganize, disperse, dissolve,
   go separate ways, let go, part, part company, release, scatter,
   separate, split up