"Jewel in the Crown" is a phrase typically used to refer to something or someone that is considered the most valuable or important part of a system or organization. Synonyms for this phrase could include "crown jewel", "prized possession", "top asset", "flagship", or "pearl". These terms are often used to describe an entity that is viewed as essential to the success or prestige of a larger entity, such as a business or government. The phrase may also be used to describe a highly-regarded personal achievement or accomplishment, such as earning a graduate degree or winning a prestigious award.