big, broad, Cheshire (AmE), Cheshire-cat, huge, large, wide
faint, feeble, slight, small
friendly, sympathetic
happy
infectious
lazy
cheesy, foolish, goofy, silly, stupid
boyish, cheeky (BrE), devilish, devious, impish, mischievous, playful, sly, teasing
Edmund looked up with an impish grin.

mocking, teasing
cocky, smug
satisfied
sheepish, shy
rueful, sardonic, wry
knowing
insane, manic
amused
evil, feral (esp. AmE), hideous, malicious, sinister, wicked, wolfish
crooked, lopsided
gap-toothed, toothless, toothy

have
He had a cheeky grin.
I wondered why Dad had a grin on his face.

crack, flash (sb), give (sb), let out (AmE)
He gave the photographer a big grin.

grin, smile
He grinned his adorable grin.

force, manage
He forced a grin despite feeling angry.

break into, curl into (AmE), form, split into
The old man's face broke into a grin.
Her lips started to form a slight grin.

fight, fight back, hide, hold back, stifle, suppress
She tried to stifle a grin.

wear
return

broaden, grow, grow broader, grow wider, widen
appear, break out (across sb's face), come across sb's face, come over sb's face, creep across sb's face, creep onto sb's face, cross sb's face, form on sb's face, spread across sb's face, spread over sb's face
A mischievous grin spread across the little girl's face.

be plastered across sb's face, be plastered on sb's face, light sb's face, light up sb's face, play on sb's face, split sb's face, tug at sb's lips
a grin tugging at the corners of his lips

disappear, fade
His wry grin faded.

turn into sth
Her grin turned into a frown.

with a grin
‘Fooled you!’ he said, with a cheeky grin.

grin at
a grin at his wife

grin of
a grin of triumph

take the grin off your face, wipe the grin off your face
Take that grin off your face!

wipe the grin off sb's face
I'll soon wipe that silly grin off her face.

broadly, widely
He appeared in the doorway grinning broadly.

slightly, weakly
crookedly
brightly, cheerfully, happily
amiably
boyishly, cheekily (BrE), devilishly, impishly, mischievously, playfully
madly, wildly
triumphantly
proudly
inanely, stupidly
nervously, sheepishly
He just stood there, tongue-tied and grinning sheepishly.

apologetically, ruefully, wryly
She grinned apologetically when she saw him.

evilly, maliciously, slyly, wolfishly
knowingly
smugly
back, down at, up at
She relaxed and grinned wickedly back at him.
He lay grinning impishly up at me.

at
He stopped eating to grin at me.

like
He just stood there, grinning like an idiot.

to
She grinned to herself at the thought.

with
They grinned with pleasure.

grin ear to ear (AmE), grin from ear to ear
She looked at us, grinning from ear to ear.

Grin is used with these nouns as the object:
grin