Emily Dickinson Lexicon

GRIN, v.i. [Sax. grinnian; G. greinen, grinsen; D. grynen, grinzen; Sw. grina; Dan. griner. In W. ysgyrnwg is a grin or snarl, and ysgorn, scorn.]

1. To set the teeth together and open the lips, or to open the mouth and withdraw the lips from the teeth, so as to show them, as in laughter or scorn. Fools grin on fools. Young.
2. To fix the teeth, as in anguish.