From the English word mystic, ultimately from Greek mystikos, meaning secret, spiritual, or initiated into sacred mysteries.
Mystic derives from the ancient Greek "mystikos," meaning one initiated into secret rites, an adjective built from "mystes" (initiate) and ultimately from "myein," to close — referring to the closed lips and eyes required of initiates in the mystery cults of antiquity. The Eleusinian Mysteries, celebrated at Eleusis near Athens for nearly two thousand years, were among the most significant religious institutions of the ancient world, and those who underwent initiation were promised a transformed understanding of life and death. To call something mystic was originally to mark it as belonging to that transformed inner circle.
Over centuries the word traveled through Latin, into medieval theological discourse (where "mystical theology" described direct experiential knowledge of the divine, as opposed to scholarly doctrine), and eventually into the broader English vocabulary of wonder, mystery, and the ineffable. The Mystic River in Massachusetts takes its name from the Algonquian people who lived near it; the city of Mystic, Connecticut became a historic whaling and shipbuilding port. In the 20th century "mystic" migrated from adjective to noun to personal identifier, carried by traditions from Tarot to yoga studios to New Age spirituality.
As a given name, Mystic is genuinely rare and genuinely bold — it belongs to a category of virtue-and-concept names like Serenity, Journey, and True that parents choose when they want a child's name to be a statement of intention. It sits in distinguished literary company: Mystic River is both the title of a Dennis Lehane novel and a Clint Eastwood film, works of great moral weight. A child named Mystic is given a name that promises depth and invites questions — an identity that refuses the ordinary.