lesson · noun C /ˈles.ən/Full view
lesson (TEACHING PERIOD)
A1 a period of time when a teacher teaches people
Dictionary examples:

How can we make science lessons more interesting?

Did you ever take piano lessons?

He gives French lessons.

Learner example:

One lesson take[s] 45 minutes. (Skills for Life (Entry 1); A1; Polish)

lesson (EXPERIENCE)
B2 an experience that teaches you how to behave better in a similar situation in the future
Dictionary examples:

There is a lesson in this tragic accident.

Losing his job was a lesson he never forgot.

We can learn important lessons from this.

Learner example:

I think he learned a valuable lesson. (First Certificate in English; B2; Turkish)

learn a/your lesson
B2 to decide not to do something again because it has caused you problems in the past
Dictionary example:

I'm not going out without my umbrella again - I've learned my lesson!

Learner example:

Actually, I am happy to hear that journalists have learned their lesson from the death of Princess Diana and try to let her children and [the] Royal family have more privacy. (First Certificate in English; B2; Chinese)

teach sb a lesson
C2 to punish someone so that they will not behave badly again
Dictionary example:

The next time she's late, go without her. That should teach her a lesson.

Learner example:

He didn't want to hurt Diane just teach her a lesson. (Certificate of Proficiency in English; C2; Dutch)

Cambridge logo