The phrase "the apple of someone's eye" is a popular idiomatic expression that refers to a person or thing that is greatly cherished or valued by someone. There are many other synonyms for this phrase, including "darling," "gem," "beloved," "pride and joy," "treasure," "dear one," "precious," "loved one," and "heartthrob." These synonyms can be used to describe a wide range of emotions and relationships, such as parental love, romantic love, and admiration for a valued possession. Regardless of which synonym is used, the sentiment remains the same - that the person or thing is cherished and held in high regard.