pupil has two meanings.
pupil can be used to address any person who is a student, a trainee, a learner, a follower, a disciple. Any person who is learning something or is being trained by some other person is called a pupil.
pupil also is the name for the small hole or opening in the eyesballs. this hole allows light to enter the eye and lets us see this beautiful word. also, right now, your pupil is allowing light to enter to your eye and thus letting you read this answer. ;)
