1. A response to a stimulus. 2. The state resulting from such a response. 3. A reverse or opposing action. 4. A tendency to revert to a former state. 5. Opposition to progress or liberalism; extreme conservatism. 6. A change or transformation in which a substance decomposes, combines with other substances, or interchanges constituents with other substances. 7. A nuclear reaction. 8. An equal and opposite force exerted by a body against a force acting upon it. 9. The response of cells or tissues to an antigen, as in a test for immunization. 10. A pattern of behavior constituting a mental disorder or personality type.
