grinsen
to grin
To smile broadly, often with visible teeth, usually in a mocking, mischievous, or self-satisfied way.
Als er den gelungenen Streich sah, musste er breit grinsen.
When he saw the successful prank, he had to grin broadly.

to grin
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to grin
To smile broadly, often with visible teeth, usually in a mocking, mischievous, or self-satisfied way.
Als er den gelungenen Streich sah, musste er breit grinsen.
When he saw the successful prank, he had to grin broadly.

The way someone grins is often described more precisely with adverbs. Typical combinations are 'breit grinsen' (to grin broadly), 'frech grinsen' (to grin cheekily), or 'hämisch grinsen' (to grin maliciously).
Er sah mich an und grinste breit.
He looked at me and grinned broadly.
The idiom 'über das ganze Gesicht grinsen' (to grin from ear to ear) describes a particularly broad and open smile that expresses great joy or amusement.
Als sie die gute Nachricht hörte, grinste sie über das ganze Gesicht.
When she heard the good news, she grinned from ear to ear.
The reflexive expression 'sich ins Fäustchen grinsen' means to be secretly pleased about something, often about someone else's misfortune.
Er grinste sich ins Fäustchen, als der Plan seines Gegners fehlschlug.
He grinned to himself when his opponent's plan failed.
to laugh
'lachen' and 'grinsen' both have to do with a happy or amused facial expression. 'lachen' is usually audible and openly shows that something is funny. 'grinsen' is a broad smile, often without a loud sound. It can seem mischievous, mocking, or self-satisfied. Learners may confuse the words because both occur in funny situations. If someone reacts loudly, you are more likely to say 'lachen'. If the facial expression is important and maybe seems a bit cheeky, 'grinsen' fits better.

Tom grinst, als er merkt, dass sein kleiner Plan funktioniert hat.
Tom grins when he realizes that his little plan has worked.
Im Büro lachen alle, weil der Kollege eine lustige Geschichte erzählt.
In the office, everyone laughs because their colleague is telling a funny story.