Any action in resisting other action or force; counter tendency; movement in a contrary direction; reverse action.
- A response to a stimulus.
- The state resulting from such a response.
- A reverse or opposing action.
- A tendency to revert to a former state.
- Opposition to progress or liberalism; extreme conservatism.
- Chemistry A change or transformation in which a substance decomposes, combines with other substances, or interchanges constituents with other substances.
- Physics A nuclear reaction.
- Physics An equal and opposite force exerted by a body against a force acting upon it.
- The response of cells or tissues to an antigen, as in a test for immunization.