Definition of "idiotism"

idiotism¹

noun
countable and uncountable, plural idiotisms
1. (now chiefly historical) Very severe mental retardation.
  Quotations
  He did not perceive that regal power, in a few generations, introduces idiotism into the noble stem […]
  1791 (date written), Mary Wollstonecraft, A Vindication of the Rights of Woman: With Strictures on Political and Moral Subjects, 1st American edition, Boston, Mass.: […] Peter Edes for Thomas and Andrews, […], published 1792
  Idiotism had long been accepted as hopeless: ‘Absolute idiocy admits of no cure,’ noted the nineteenth-century psychiatrist George Man Burrows (1771–1846).
  1997, Roy Porter, The Greatest Benefit to Mankind, Folio Society, published 2016, page 488
2. A foolish utterance.
  Quotations
  […] that clear soprano, in nursery, rings out a shower of innocent idiotisms over the half-stripped baby, and suspends the bawl upon its lips.
  1863, Sheridan Le Fanu, The House by the Churchyard

idiotism²

noun
plural idiotisms
1. Idiom.
2. An overly literal translation of an idiom.