Fig. to grind or bite noisily with one's teeth. Bill clenched his fists and gnashed his teeth in anger.The wolf gnashed its teeth and chased after the deer.
Fig. a show of anger or dismay. (Biblical: "weeping, wailing, and gnashing of teeth.") After a little gnashing of teeth and a few threats, the boss calmed down and became almost reasonable.
to show you are angry or annoyed about something bad that you cannot do anything to stop His advisers are gnashing their teeth in frustration because he refuses to attack his opponent on foreign policy issues.
Usage notes: also used in the form gnashing of teeth: The first test-tube baby was born in 1978, to considerable gnashing of teeth.
Express a strong emotion, usually rage, as in When Jonah found out he was not going to be promoted, he gnashed his teeth. This expression is actually redundant, since gnash means "to strike the teeth together." Edmund Spenser used it in The Faerie Queene (1590): "And both did gnash their teeth." [Late 1500s]