More silly than something else.
Sillier is a fun word that means something is more funny or not serious than something else.
Examples:
The clown is sillier than the teacher.
My joke is sillier than yours.
The dog's hat is sillier than the cat's hat.
The sillier the better!
Eating ice cream for dinner is sillier than eating vegetables.
The sillier the hat, the more fun it is to wear!