Grin http://www.synonym.com/synonyms/smile/
A synonym for the word grin is smile. An antonym for the word grin is frown. Synonyms: gleam, glow, grin, laugh, radiate, shine, smirk Antonyms: frown, scowl
The word 'grin' is both a verb and a noun.The noun 'grin' is a singular, common, concrete noun; a word for a wide smile; a word for a thing.The noun form of the verb to grin is the gerund, grinning.
He couldn't help but grin from ear to ear when he saw his surprise birthday party.
She couldn't help but grin when she saw her surprise birthday party waiting for her.
grin
Grin
a grin
smirk
Grin.
Every word has a purpose, which it fulfills successfully. There might be a better word than grin in some context, but you haven't stated any context. You would have to tell us what purpose you have in mind, which is not quite fulfilled by the word grin.
Grin or smirk