grin

Etymology 1

Before 1000 CE - From Middle English grinnen, from Old English grennian, of Germanic origin and probably related to groan. Compare to Old High German grennan (“to mutter”) and Danish grine (“to show one's teeth, to laugh”)

noun

1. A smile in which the lips are parted to reveal the teeth.
   When the ceremony was finished a wide grin broke across his face, and it was that grin she saw, relieved and happy all at once. 1997, Linda Howard, Son of the Morning, Simon & Schuster, page 364
   When my son appeared at the door the next day with his schoolbag on his back, the Professor broke into a wide grin and opened his arms to embrace him. 2003, Yoko Ogawa, The Housekeeper and the Professor

verb

1. (intransitive) To smile, parting the lips so as to show the teeth.
   Why do you grin? Did I say something funny?
   ‘No,’ said Luke, grinning at her. ‘You're not dull enough! […] What about the kid's clothes? I don't suppose they were anything to write home about, but didn't you keep anything? A bootee or a bit of embroidery or anything at all?’ 1963, Margery Allingham, chapter 15, in The China Governess
2. (transitive) To express by grinning.
   She grinned pleasure at his embarrassment.
3. (intransitive, dated) To show the teeth, like a snarling dog.
4. (transitive) To grin as part of producing a particular facial expression, such as a smile or sneer.
   He grinned a broad smile when I told him the result.
   He grinned a cruel sneer when I begged him to stop.

Etymology 2

From Old English grin.

noun

1. (obsolete) A snare; a gin.
   c. 14th century, unknown author (originally attributed to Geoffrey Chaucer), Remedy of Love Like a bridde that hasteth to the grynne.