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enfant sauvage

British  
/ ɑ̃fɑ̃ sovaʒ /

noun

  1. a person given to naive, undisciplined, or unpredictable behaviour, largely because of youth and inexperience

"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Etymology

Origin of enfant sauvage

C20: literally: wild child