One who benights; something that causes darkness or ignorance; a rare term.
From benight plus the -er suffix meaning 'one who does.' This is an extremely rare noun form that appears almost never in modern English.
Benighter is theoretically a word—something that makes things dark or ignorant—but it's so rare that you could read hundreds of books and never encounter it, proving that grammatically correct words don't always survive in actual use.
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