muster out of
1. To leave or resign from the military. My father served in the Marines for twenty years before mustering out in 1993.
2. To discharge someone from the military. In this usage, a noun or pronoun can be used between "muster" and "out." He sued the Navy after he was mustered out in the late 80's for his sexual orientation. They threatened to muster him out if he revealed the information to the public.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
muster out of something
to be discharged from military service. He mustered out of the service before his time was up. I want to know how I can muster out too.
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.