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)
n.
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.
extinction (ĭk-stĭngk'shən)
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The disappearance of a species from the Earth.
Note: The fossil record tells us that 99.9 percent of all species that ever lived are now extinct.