Lessen or Lesson?
Your choice!
Lessen
Exemple : ‘’In order to lessen the pain I suggest you put a bandage on.’’
"Lessen" and "lesson" are commonly confused although they have completely different uses. To "lessen" means "to reduce."
Lesson
Exemple : ‘’The maths lesson this morning was extremely boring.’’
"Lesson" is used as a noun to denote a period of time during which something is taught or an experience which teaches you something.