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.

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

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


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).


  1. A lack of or abnormality in something necessary for normal functioning; a deficiency or imperfection.
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