grin 
(grĭn)
(grĭn)v. grinned, grin·ning, grins
v.intr.
To smile broadly, often baring the teeth, as in amusement, glee, embarrassment, or other strong emotion.
v.tr.
To express with a grin: I grinned my approval.
n.
1. The act of grinning.
2. The facial expression produced by grinning.
[Middle English grennen, to grimace, from Old English grennian.]
grinner n.
grinning·ly adv.