Silliness is when someone acts or talks in a way that is not serious and is funny or not sensible.
Silliness is usually seen as lighthearted and can make people laugh.
Examples:
Her silliness made everyone laugh.
I don't like his silliness when we are trying to work.
The silliness of the clown made the children happy.
The silliness of the dog wearing a hat was very funny.
The silliness of the idea made everyone laugh.
The silliness of the monkey wearing glasses was very funny.