calliope n.

in classical mythology a nymph, mother of Arcas by Zeus, turned to a bear by Hera, from Greek kallistos, superlative of kalos "beautiful, beauteous, noble, good," and its derived noun kallos "beauty," from *kal-wo-, which is of uncertain origin, perhaps related to Sanskrit kalyana "beautiful." The usual combining form in Greek was kalli- "beautiful, fine, happy, favorable;" kalo- was a later, rarer alternative form. Also a name given to the fourth moon of Jupiter in 17c. but not widely used before mid-19c. Feminized as a proper name as Callista.

Proto-Indo-European root meaning "to speak."

It forms all or part of: advocate; avocation; calliope; convocation; epic; equivocal; equivocation; evoke; invoke; provoke; revoke; univocal; vocabulary; vocal; vocation; vocative; vociferate; vociferous; voice; vouch; vox; vowel.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit vakti "speaks, says," vacas- "word;" Avestan vac- "speak, say;" Greek eipon (aorist) "spoke, said," epos "word;" Latin vocare "to call," vox "voice, sound, utterance, language, word;" Old Prussian wackis "cry;" German er-wähnen "to mention."