lock nut

or lock·nut

noun Machinery.
  1. a nut specially constructed to prevent its coming loose, usually having a means of providing extra friction between itself and the screw.
  2. Also called jam nut. a thin supplementary nut screwed down upon a regular nut to prevent its loosening.

Origin of lock nut

First recorded in 1860–65
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Examples from the Web for locknut

Historical Examples of locknut

  • A locknut is used beneath the notched nut to hold the adjustment.

  • A locknut is used to hold the screw in any desired position.

  • When the bolt has been screwed down sufficiently tight a locknut may be put on, or the first nut soldered to the end of the bolt.

British Dictionary definitions for locknut


  1. a supplementary nut screwed down upon a primary nut to prevent it from shaking loose
  2. a threaded nut having a feature, such as a nylon insert, to prevent it from shaking loose
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