Quick answer
Kallisto is a girl name meaning "most beautiful".
Meaning and history
This name is derived from Greek κάλλιστος (kallistos) meaning "most beautiful", a derivative of καλός ( kalos ) meaning "beautiful". In Greek mythology Kallisto was a nymph who was loved by Zeus. She was changed into a she-bear by Hera, and subsequently became the Great Bear constellation. This was also an ancient Greek personal name.
Notes and context
Usage: greek mythology, ancient greek | Ancient Greek: Καλλιστώ