Dictionary.com
definitions

idiot savant

[id-ee-uh t sa-vahnt, suh-vant, sav-uh nt; French ee-dyoh sa-vahn]
noun, plural id·i·ot sa·vants, French id·i·ots sa·vants [ee-dyoh sa-vahn] /i dyoʊ saˈvɑ̃/. Psychiatry.
  1. a mentally defective person with an exceptional skill or talent in a special field, as a highly developed ability to play music or to solve complex mathematical problems mentally at great speed.

Origin of idiot savant

1925–30; < French: literally, learned idiot
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
British Dictionary definitions for idiot savant

idiot savant

noun plural idiots savants (ˈiːdjəʊ sæˈvɑ̃) or idiot savants
  1. a person with learning difficulties who performs brilliantly at some specialized intellectual task, such as giving the day of the week for any calendar date past or present

Word Origin for idiot savant

C19: from French: knowledgeable idiot
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
idiot savant in Medicine

idiot savant

[să-vänt′]
n. pl. idiot savants
  1. A mentally retarded person who exhibits genius in a highly specialized area, such as mathematics.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.