A supplementary nut that is screwed down on a primary nut to prevent it from loosening.
A kind of nut which, when screwed onto a bolt, locks itself into place without need for a lock washer.
A nut which provides extra resistance to vibration loosening by either providing some form of prevailing torque, or, in free spinning nuts, by deforming and/or biting into mating parts when fully tightened. SYN. locknut.