locknut
nounA usually thin nut screwed down on another nut to prevent it from loosening.
nounA self-locking nut.
nounA supplementary nut screwed down upon another to prevent it from shaking loose; a jam-nut, check-nut, or pinch-nut.
nouna supplementary nut that is screwed down on a primary nut to prevent it from loosening; a check nut.
nounA second
supplementary nut that is screwed down on a primary nut to prevent it from loosening