verb
BAD : Many species are becoming extinguished.
GOOD : Many species are becoming extinct.
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extinguish = make something stop burning: 'Before entering the factory, please make sure that all cigarettes have been properly extinguished.'
extinct = (of a type of animal or plant) completely non-existent, because every single one has died or been killed: 'If nothing is done to save the whales now, the species will soon become extinct.'