from
The Collaborative International Dictionary of English v.0.48
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]