Gnash
/næʃ/
Definition 1 of 1
Pro Tip 1/3Expression of Anger
Use 'gnash' when describing an intense emotional response, especially anger. 
The villain gnashed his teeth as the hero escaped.
Pro Tip 2/3Physical Discomfort
'Gnash' can also convey a reaction to physical pain or discomfort. 
She gnashed her teeth silently as the doctor stitched her wound.
Pro Tip 3/3Intensity of Emotion
The word emphasizes a strong emotion, not a mild annoyance or discomfort. 
Overcome with grief, he gnashed his teeth, unable to speak.