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adjective, un·sound·er, un·sound·est.
  1. not sound; unhealthy, diseased, or disordered, as the body or mind.
  2. decayed or impaired, as timber or foods; defective.
  3. not solid or firm, as foundations.
  4. not well-founded or valid; fallacious: an unsound argument.
  5. easily broken; light: unsound slumber.
  6. not financially strong; unreliable: an unsound corporation.

Origin of unsound

Middle English word dating back to 1275–1325; see origin at un-1, sound2
Related formsun·sound·ly, adverbun·sound·ness, noun

Synonyms for unsound

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Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

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British Dictionary definitions for unsound


  1. diseased, weak, or unstableof unsound mind
  2. unreliable or fallaciousunsound advice
  3. lacking solidity, strength, or firmnessunsound foundations
  4. of doubtful financial or commercial viabilityan unsound enterprise
  5. (of fruit, timber, etc) not in an edible or usable condition
Derived Formsunsoundly, adverbunsoundness, noun
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

Word Origin and History for unsound

early 14c., of persons, "diseased, wounded," from un- (1) "not" + sound (adj.). Cf. Middle Low German unsund, Middle Dutch ongesont, German ungesund. Meaning "morally corrupt" is recorded from c.1300; that of "not mentally healthy" is from 1540s. Sense of "not based on reasoning or fact" is attested from 1590s.

Online Etymology Dictionary, © 2010 Douglas Harper