An archaic or obsolete form of 'engine'; a mechanical device, weapon, or instrument of power.
From Old French engin, from Latin ingenium meaning ingenuity or a clever device. This is an older spelling that fell out of use as 'engine' became standardized.
Medieval writers called all kinds of devices 'engins'—from battering rams to water mills—because the word meant 'clever contraption' before we narrowed it to mean motors!
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