The practice of deceiving or tricking people; deceptive behavior or trickery.
From 'gull' (to deceive) plus the suffix '-ery' (meaning the practice or characteristic behavior of something). This follows medieval English naming conventions for habitual actions.
Medieval English loved '-ery' for naming vices and practices—'witchery,' 'tomfoolery,' 'trickery'—as if adding the suffix made them official categories of human misbehavior!
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