Pupil

n. student; opening in the center of the iris of the eye (Anatomy)

The pupil (Latin pupilla "little doll" > pupa "doll") is the variable-sized, black circular or slit shaped opening in the center of the iris that regulates the amount of light that enters the eye. It appears black because most of the light entering the pupil is absorbed by the tissues inside the eye.
See more at Wikipedia.org...

Pupil /pu·pil/ the opening in the center of the iris through which light enters the eye.pu´pillary Adie's pupil tonic p. [more]Pupil - Community and Resources

Noun
1. a learner who is enrolled in an educational institution
(synonym) student, educatee
(hypernym) enrollee
(hyponym) art student
(member-holonym) teacher-student relation
2. contractile aperture in the iris of the eye
(hypernym) aperture
(part-holonym) iris
3. a young person attending school (up through senior high school)
(synonym) schoolchild, school-age child
(hypernym) young person, youth, younker, spring chicken
(hyponym) boarder

n. pupil, ward, cheeper