What is the apple of one’s eye? July 29, 2020 by Pamela Landy The apple of one’s eye is the pupil, which was likened to an apple because, in the ninth century, it was believed to be a solid round mass. Related Answers What was Lincoln’s “eye for an eye” order issued during the Civil War? When was the first public opinion poll taken? What was the Code of Hammurabi? Where did the part of the throat known as the Adam’s apple get its name? Whom did private eye Matt Helm work for?