from The American Heritage® Dictionary of the English Language, 4th Edition
- intransitive v. To clench or grind one's teeth.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- v. To grind the teeth, especially involuntarily or during sleep.
Back-formation from bruxism.(American Heritage® Dictionary of the English Language, Fourth Edition)
Back-formation from bruxism, from Ancient Greek βρυγμός (brigmós, "grinding [teeth]"). (Wiktionary)