— reactional , adj. — reactionally , adv.
/ree ak"sheuhn/ , n.
1. a reverse movement or tendency; an action in a reverse direction or manner.
2. movement in the direction of political conservatism or extreme rightism.
3. action in response to some influence, event, etc.: the nation's reaction to the President's speech.
4. Physiol. action in response to a stimulus, as of the system or of a nerve, muscle, etc.
5. Med.
a. the action caused by the resistance to another action.
b. a return to the opposite physical condition, as after shock, exhaustion, or chill.
6. Bacteriol. , Immunol. the specific cellular response to foreign matter, as in testing for allergies.
7. Chem. the reciprocal action of chemical agents upon each other; chemical change.
8. Also called nuclear reaction . Physics. a process in which a nucleus that is bombarded by a photon, particle, or other nucleus, emits a nucleon, alpha particle, or the like, without a significant change in its atomic weight.
9. Mech. the instantaneous response of a system to an applied force, manifested as the exertion of a force equal in magnitude but opposite in direction to the applied force.
10. Com. a decline in the market after an advance in prices.
[ 1635-45; RE- + ACTION, modeled on react ]