A person who depraves or corrupts others morally; one who leads others toward wickedness.
From deprave + -er (agent suffix). The -er ending creates nouns meaning 'one who does X,' as in 'teacher,' 'runner,' or 'baker.'
The -er suffix is so old and productive that it's one of the first ways children learn to make new words—'one who bakes is a baker'—and it's been working this way in English for over a thousand years.
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