A diminutive of Callie or Calista, from Greek roots meaning "beautiful."
Cally is most commonly understood as a diminutive or variant of names rooted in the Greek kalos or kallos, meaning "beautiful" — the root that gives us Calliope ("beautiful voice," the muse of epic poetry), Callisto ("most beautiful," the nymph transformed into a bear by Zeus and placed among the stars as Ursa Major), and Callista ("most beautiful"). All of these names share that warm Greek aesthetic that places beauty — particularly the beauty of sound and form — at the center of a person's identity. Calliope, the chief of the nine Muses, presided over eloquence and epic poetry; Hesiod and Ovid both invoked her, and she is the muse said to have guided Homer's hand as he composed the Iliad and the Odyssey.
A child named Cally, then, is in some sense a descendant of that long tradition of artistic inspiration. Separately, Cally appears in Scottish Gaelic usage as a variant of Caileag, simply meaning "girl" — a homely, affectionate term that gives the name an entirely different, earthier feel in the Celtic world. In popular culture, Cally was a character in the original British science-fiction series Blake's 7 (1978–1981), a telepathic guerrilla fighter whose quiet intensity gave the name a hint of science-fictional gravitas.
Today Cally functions primarily as a standalone given name or as a nickname for Caroline, Calliope, or Callista. Its two syllables are bright and easy, carrying both the beauty of its Greek roots and the friendly familiarity of a name that has always felt approachable — lovely without being showy, classical without being heavy.