From the Oxford English Dictionary
Forms: late Middle English methamorphosyos, 15 c. metamorphosys, 15– metamorphosis.
Etymology: < classical Latin metamorphōsis (only with reference to the work by Ovid; in post-classical Latin in sense 1a (5th cent.)) < Hellenistic Greek μεταμόρϕωσις < μετα-meta- prefix + μόρϕωσις morphosis n., after μεταμορϕοῦν to transform. Compare Middle French, French métamorphose (c1365 as a translation of the title of the work by Ovid; 1493 in Middle French in sense 1a; 1668 in sense 2; 1736 in sense 3a). Compare also Italian metamorfosi (1499), Spanish metamorfosis (c1620).The first Latin use is in the plural form Metamorphōsēs as the title of a poem by Ovid in the classical tradition of tales about transformations of gods or humans into the shapes of animals, plants, or inanimate objects. Subsequent uses in Latin, as well as the earliest uses in English, allude to or are strongly influenced by Ovid’s poem. English forms of the title of the poem are numerous until the 16th cent., from which time only the standard singular and plural forms are used:
c1390 Chaucer Man of Law’s Tale B.93 Me were looth be likned‥To Muses that men clepe Pierides; Methamorphosios [v.rr. Methamorphoseos, Metham orphaseos, Methanorphoseos, Methemore phees, Meche more phees] woot what I mene.
Greek μεταμορϕοῦν has a wider application, and appears in the gospels with the sense ‘transfigure’ transfigure v. 1b; some examples of the use of metamorphosis and related words in post-classical Latin reflect this gospel use (compare metamorphist n. 1).
1a. The action or process of changing in form, shape, or substance; esp. transformation by supernatural means.