gristbitung, f.n: a gnashing of the teeth.
Someone asked where you can find this word in OE. According to the OE Corpus, there are 28 occurrences, which include the poem Christ and Satan and various prose texts — Ælfric’s sermon on Judgment Day, a letter for Wulfstan, the gospel of Matthew, Gregory’s Dialogues, various homilies. Example sentence: ‘And on helle bið eagena wop and toþa gristbitung‘ (‘And in hell there is weeping of eyes and gnashing of teeth’).
In the poems Judith and Juliana you find the verb gristbātian, which is of course what you do when you want to be subtle about waking up your lech general in the morning because he might still be busy with last night’s sexy dinner guest.