1. 1. The act or an instance of transforming.
   2. The state of being transformed.
2. A marked change, as in appearance or character, usually for the better.
3. Mathematics.
   1. Replacement of the variables in an algebraic expression by their values in terms of another set of variables.
   2. A mapping of one space onto another or onto itself.
4. Linguistics.
   1. A rule that systematically converts one syntactic form or form of a sentence into another.
   2. A construction or sentence derived by such a rule; a transform.
5. Genetics.
   1. The change undergone by an animal cell upon infection by a cancer-causing virus.
   2. The alteration of a bacterial cell caused by the transfer of DNA from another bacterial cell, especially a pathogen.

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.