1. A transformation, as by magic or sorcery.
2. A marked change in appearance, character, condition, or function.
3. Biology. A change in the form and often habits of an animal during normal development after the embryonic stage. Metamorphosis includes, in insects, the transformation of a maggot into an adult fly and a caterpillar into a butterfly and, in amphibians, the changing of a tadpole into a frog.
4. Pathology. A usually degenerative change in the structure of a particular body tissue.

[Latin metamorphōsis, from Greek, from metamorphoun, to transform : meta-, meta- + morphē, form.]

The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.