1. The act of modifying or the condition of being modified. 2. A result of modifying. 3. A small alteration, adjustment, or limitation. 4. Biology Any of the changes in an organism caused by environment or activity and not genetically transmissable to offspring. 5. Linguistics a. A change undergone by a word that is borrowed from another language. b. A phonological change undergone by a word or morpheme when it is used in a construction, as the change of will to 'll in they'll.