Definition of "grin"

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

‘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

Grinned horrible a ghastly smile.

1667, John Milton, “Book II”, in Paradise Lost. […], London: […] [Samuel Simmons], […]; republished as Paradise Lost in Ten Books: […], London: Basil Montagu Pickering […], 1873,

"Mid-Lent, and the Enemy grins," remarked Selwyn as he started for church with Nina and the children. Austin, knee-deep in a dozen Sunday supplements, refused to stir; poor little Eileen was now convalescent from grippe, but still unsteady on her legs; her maid had taken the grippe, and now moaned all day: "Mon dieu! Mon dieu! Che fais mourir!"

1907 August, Robert W[illiam] Chambers, chapter IV, in The Younger Set, New York, N.Y.: D. Appleton & Company

The pangs of death do make him grin.

1591 (date written), William Shakespeare, “The Second Part of Henry the Sixt, […]”, in Mr. William Shakespeares Comedies, Histories, & Tragedies. […] (First Folio), London: […] Isaac Iaggard, and Ed[ward] Blount, published 1623, [Act III, scene iii]

They burned the old gun that used to stand in the dark corner up in the garret, close to the stuffed fox that always grinned so fiercely. Perhaps the reason why he seemed in such a ghastly rage was that he did not come by his death fairly. And why else was he put away up there out of sight?—and so magnificent a brush as he had too.

1879, R[ichard] J[efferies], chapter 1, in The Amateur Poacher, London: Smith, Elder, & Co., […]

Like a bridde that hasteth to the grynne.

c. 14th century, unknown author (originally attributed to Geoffrey Chaucer), Remedy of Love