[noun dee-fekt, dih-fekt; verb dih-fekt]
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  1. a shortcoming, fault, or imperfection: a defect in an argument; a defect in a machine.
  2. lack or want, especially of something essential to perfection or completeness; deficiency: a defect in hearing.
  3. Also called crystal defect, lattice defect. Crystallography. a discontinuity in the lattice of a crystal caused by missing or extra atoms or ions, or by dislocations.
verb (used without object)
  1. to desert a cause, country, etc., especially in order to adopt another (often followed by from or to): He defected from the U.S.S.R to the West.

Origin of defect

1375–1425; late Middle English < Latin dēfectus failure, weakness, equivalent to dēfec- variant stem of dēficere to run short, fail, weaken (see deficient) + -tus suffix of v. action
Related formsde·fect·i·ble, adjectivede·fect·i·bil·i·ty, nounde·fect·less, adjectivenon·de·fect·ing, adjectivepre·de·fect, nounre·de·fect, verb (used without object)

Synonym study

1. Defect, blemish, flaw refer to faults that detract from perfection. Defect is the general word for any kind of shortcoming or imperfection, whether literal or figurative: a defect in eyesight, in a plan. A blemish is usually a defect on a surface, which mars the appearance: a blemish on her cheek. Flaw is applied to a defect in quality, caused by imperfect structure (as in a diamond) or brought about during manufacture (as in texture of cloth, in clearness of glass, etc.). Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

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British Dictionary definitions for defect


noun (dɪˈfɛkt, ˈdiːfɛkt)
  1. a lack of something necessary for completeness or perfection; shortcoming; deficiency
  2. an imperfection, failing, or blemish
  3. crystallog a local deviation from regularity in the crystal lattice of a solidSee also point defect, dislocation (def. 3)
verb (dɪˈfɛkt)
  1. (intr) to desert one's country, cause, allegiance, etc, esp in order to join the opposing forces
Derived Formsdefector, noun

Word Origin for defect

C15: from Latin dēfectus, from dēficere to forsake, fail; see deficient
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 defect

early 15c., from Middle French defect and directly from Latin defectus "failure, revolt, falling away," noun use of past participle of deficere "to fail, desert" (see deficient).


1570s, from Latin defectus, past participle of deficere "to fail, desert" (see defect (n.)). Related: Defected; defecting.

Online Etymology Dictionary, © 2010 Douglas Harper

defect in Medicine


[dēfĕkt′, dĭ-fĕkt]
  1. A lack of or abnormality in something necessary for normal functioning; a deficiency or imperfection.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.