/ik stingk"sheuhn/ , n.
1. the act of extinguishing.
2. the fact or condition of being extinguished or extinct.
3. suppression; abolition; annihilation: the extinction of an army.
4. Biol. the act or process of becoming extinct; a coming to an end or dying out: the extinction of a species.
5. Psychol. the reduction or loss of a conditioned response as a result of the absence or withdrawal of reinforcement.
6. Astron. the diminution in the intensity of starlight caused by absorption as it passes through the earth's atmosphere or through interstellar dust.
7. Crystall. , Optics. the darkness that results from rotation of a thin section to an angle (extinction angle) at which plane-polarized light is absorbed by the polarizer.
[ 1375-1425; late ME extinccio ( u ) n ex ( s ) tinction- (s. of ex ( s ) tinctio ). See EXTINCT, -ION ]