'Grinning' definitions:

Definition of 'grinning'

noun

A facial expression characterized by turning up the corners of the mouth; usually shows pleasure or amusement [syn: smile, smiling, grin, grinning]

From: GCIDE

Grin \Grin\, v. i. [imp. & p. p. Grinned; p. pr. & vb. n. Grinning.] [OE. grinnen, grennen, AS. grennian, Sw. grina; akin to D. grijnen, G. greinen, OHG. grinan, Dan. grine. [root]35. Cf. Groan.]
1. To show the teeth, as a dog; to snarl. [1913 Webster]
2. 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, scorn, or pain. [1913 Webster]
The pangs of death do make him grin. --Shak. [1913 Webster]