re·ac·tion 
(rē-ăkshən)
(rē-ăkshən)n.
1.
a. A response to a stimulus.
b. The state resulting from such a response.
2. A reverse or opposing action.
3.
a. A tendency to revert to a former state.
b. Opposition to progress or liberalism; extreme conservatism.
4. Chemistry A change or transformation in which a substance decomposes, combines with other substances, or interchanges constituents with other substances.
5. Physics A nuclear reaction.
6. Physics An equal and opposite force exerted by a body against another body that is exerting a force on it.
7. The response of cells or tissues to an antigen, as in a test for immunization.
- propitious
- propitiously
- propitiousness
- propjet
- proplastid
- propofol
- propolis
- proponent
- proportion
- proportionable
- proportionably
- proportional
- proportionality
- proportionally
- proportional representation
- proportionate
- proportionately
- proportionateness
- proportioner
- proportionment
- proposal
- propose
- proposer
- proposition
- propositional