From Longman Dictionary of Contemporary Englishgringrin1 /ɡrɪn/ ●●○ verb (grinned, grinning) [intransitive] 1 
SMILEto smile widelygrin at She grinned at me, her eyes sparkling.grin broadly/widely He walked out of the pool, grinning widely.grin like He was grinning like an idiot (=grinning in a silly way).grin from ear to ear (=grin very widely)2 → grin and bear it→ See Verb table
SMILEto smile widelygrin at She grinned at me, her eyes sparkling.grin broadly/widely He walked out of the pool, grinning widely.grin like He was grinning like an idiot (=grinning in a silly way).grin from ear to ear (=grin very widely)2 → grin and bear it→ See Verb tableExamples from the Corpus
grin• "I guess we'll soon find out who's better, " she said with a grin.• There was what may have been a bishop's mitre on the skull, which grinned amiably up at us.• Then they both began to grin, and finally laughed out loud.• Yanto grinned and twisted the throttle again.• I grin at him with my eyes and check my watch.• She kept grinning at me as if we were old friends.• She sat back down again, grinning broadly.• He grins cockily and knowingly, holding a couple of arrows in his hand-he's Cupid, after all.• She was holding the baby, and grinning from ear to ear.• Mr Barraza was grinning, his teeth bright, his bulk overshadowing both of us.• 'I've been a complete idiot', grinned Ian.• Grinning shyly, he offered her a drink.grin from ear to ear• He was grinning from ear to ear and pointing his finger up to the flies.gringrin2 ●●○ noun [countable] SMILEa wide smile He came into the room with a friendly grin on his face.wide/broad/big etc grin ‘Of course, ’ he agreed with a wide grin. → wipe the grin off somebody’s face at wipe1(7)COLLOCATIONSadjectivesa big/huge etc grinHe walked towards me with a big grin.a wide/broad grin‘It was great!’ she shouted, with a wide grin.a toothy grin (=one that shows your teeth a lot)The man gave a large toothy grin.a mischievous grin'Let's play a trick on her’ he suggested with a mischievous grin.a silly grin‘Wipe that silly grin off your face!’ the teacher shouted.a friendly grinSam greeted her with a friendly grin.a delighted grin‘I've managed to fix it!’ she said, with a delighted grin.a sheepish grin (=an embarrassed grin because you have done something silly or wrong)"Sorry", he said with a sheepish grin.a sly grinA sly grin crossed his face.verbsgive a grinBill read the letter and gave a sudden grin.break/split into a grinThe old man’s face broke into a grin.flash somebody a grin (=smile quickly at someone)Flashing me a grin over her shoulder, she got into the car.a grin spreads (=a wide smile covers someone's face)A self-satisfied grin spread across his face.a grin widens (=someone starts smiling even more)Marcus's amused grin widened.phrasesa grin on somebody’s faceHe looked at Sarah, a big grin on his face. Examples from the Corpus
grin• And the big grin was back with a vengeance.• Death could pop up anytime, a jarring jack-in-the-box with a fixed, bloody grin.• Her face broke into a delighted grin.• William gave her a friendly grin as he walked past.• He gave them a huge grin and blew them a kiss.• Tommy shoots me a little grin.• I was very shy but his mischievous grin put me at my ease and we strolled along behind Sally and her beau.• The television camera captured his sheepish grin as he stepped from the train.• So maybe he already had the rundown on me when he gave me that sexy sneaky grin that day.• The grin vanished like magic, her whole body stiffening in antipathy as her eyes locked with fathomless brown ones.• Joel gave her a wicked grin.• And wry grins on their faces.wide/broad/big etc grin• Karen looks back and flashes a big grin.• Monday, the Colonel came back to lunch with a big grin on his face.• For once, his big grin was missing.• Big men with big grins slumped half-sideways on their seats, shouting remarks to their neighbours.Origin grin1 Old English grennian 