early 15c., from Latin extinctionem/exstinctionem (nominative extinctio/exstinctio), noun of action from past participle stem of extinguere/exstinguere (see extinguish). Originally of fires, lights; figurative use, of wiping out a material thing (a debt, a person, a family, etc.) from early 17c.; of species by 1784.
extinction ex·tinc·tion (ĭk-stĭngk'shən)
Progressive reduction in the strength of the conditioned response in successive conditioning trials during which only the conditioned stimulus is presented and the unconditioned stimulus is omitted. See absorbance.