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1.
A person who will leave a place, party, house etc unannounced and is optionally quiet about the act of leaving. Also, as opposed to an intruder, will leave something behind such as a jacket, shoes, hat etc.
Jessica "Hey where did my dad go?"

Kyle "I think I heard the door he probably left"

Jessica "what an untruder"
by Synonym Sally June 25, 2010