metamorphosis

Short definition from Wiktionary

Noun

1. 1
   A transformation, such as one performed by magic.
2. 2
   A noticeable change in character, appearance, function, or condition.
3. 3
   A change in the form and often habits of an animal after the embryonic stage during normal development (e.g. the transformation of a caterpillar into a butterfly or a tadpole into a frog).
4. 4
   A change, usually degenerative, in the structure of a specific body tissue.