A dialectal or regional term, possibly related to benches or seating structures in specific communities.
Possibly from Old English benc (bench) with dialectal pronunciation, or from an unrelated word altogether. The etymology is highly speculative given the word's obscurity.
Words that could be 'bench' with a strange accent or 'bensh' as its own thing reveal how language variation can make us uncertain whether we're looking at spelling variation or whole different words.
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