Grin as slang means a big smile that shows you feel happy, pleased, or excited. People often use it in informal talk to describe feeling good.
He had a grin after the good news.
A grin spread over her face quickly.
Grin can also mean to show your teeth in a way that is not friendly. Animals like dogs do this to show they may be angry or to warn others. People can do this too when angry or serious.
The dog grinned to scare the stranger.
He grinned in anger at the man.
Sometimes a grin is not happy but forced or nervous. This kind of grin can show people feel shy, uncomfortable, or embarrassed. It is not a full happy smile.
He gave a nervous grin before speaking.
Her grin showed she felt shy.
Sometimes to grin means to smile in a way that shows you are amused or have a secret joke. This kind of grin is a bit sly or playful, like a smirk.
He grinned after telling the joke.
She grinned at her clever plan.
A grin can sometimes show pain or discomfort but is mixed with a smile to hide the feeling. People use it to be brave or polite even when they hurt inside.
He grinned through the pain bravely.
She grinned, hiding her hurt feelings.
