One who's taught where light enters (5)
I believe the answer is:
pupil
'one' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for pupil that I've seen before include "part of my anatomy" , "Learner at educational institution" , "Schoolchild; part of eye" , "One in the eye or in place of learning" , "One studying" .)