pupilyoudaoicibaDictYouDict[pupil 词源字典]
pupil: [14] Latin pūpus and pūpa meant respectively ‘boy’ and ‘girl’ (pūpa was applied by the Swedish naturalist Linnaeus to ‘chrysalises’, the underlying link being ‘undeveloped creature’, and English adopted it as pupa [19]). The diminutive derivatives pūpillus and pūpilla denoted ‘orphan’, a sense which remained with pūpill- as it passed via Old French pupille into English as pupil. ‘Person being taught’ did not emerge until the 16th century.

The application of the word to the ‘black aperture in the eye’, which reached English in the mid-16th century, goes back to Latin pūpilla, which was also used for ‘doll’ – the notion being that if you stand close to someone and look into their eyes, you can see yourself reflected in the pupils like a little ‘doll’.

=> pupa, puppet, puppy[pupil etymology, pupil origin, 英语词源]
pupil (n.1)youdaoicibaDictYouDict
"student," late 14c., originally "orphan child, ward," from Old French pupille (14c.) and directly from Latin pupillus (fem. pupilla) "orphan child, ward, minor," diminutive of pupus "boy" (fem. pupa "girl"), probably related to puer "child," possibly from PIE *pup-, from root *pu- "to swell, inflate." Meaning "disciple, student" first recorded 1560s. Related: Pupillary.
pupil (n.2)youdaoicibaDictYouDict
"center of the eye," early 15c. (in English in Latin form from late 14c.), from Old French pupille (14c.), from Latin pupilla, originally "little girl-doll," diminutive of pupa "girl; doll" (see pupil (n.1)), so called from the tiny image one sees of himself reflected in the eye of another. Greek used the same word, kore (literally "girl"), to mean both "doll" and "pupil of the eye;" and compare obsolete baby "small image of oneself in another's pupil" (1590s), source of 17c. colloquial expression to look babies "stare lovingly into another's eyes."
Self-knowledge can be obtained only by looking into the mind and virtue of the soul, which is the diviner part of a man, as we see our own image in another's eye. [Plato, "Alcibiades," I.133]