grin

Concise Oxford English Dictionary © 2008 Oxford University Press:
grin/ɡrɪn/

▶verb (grins, grinning, grinned)

• 1 smile broadly.

• 2 grimace grotesquely in a way that reveals the teeth.

▶noun a broad smile.

– phrases
grin and bear it suffer pain or misfortune in a stoical manner.

– derivatives
grinner noun,
grinning adjective,
grinningly adverb.

– origin OE grennian ‘bare the teeth in pain or anger’, of Gmc origin; prob. rel. to groan.