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1.
1. Crazy; insane; mad.
2. Crazy person; a lunatic.

From Hebrew via Yiddish meshugener, from meshuge (crazy) + -er (masculine singular person suffix)

Often pronounced without final -r, influenced by both Yiddish gender inflection and non-rhotic American dialectal pronunciation.
I was sitting there eating my breakfast when this meshuggener burst in the front door of the restaurant and tried to take us all hostage.
by bluegrassfan February 01, 2005