The quality of being full of cunning tricks and deception; the state of being deceitful and sly.
From guile (deceit, trickery from Old French guile) + -ful + -ness suffix. The word evolved from French roots meaning 'deception' to describe craftiness as a characteristic trait.
Medieval merchants were so skilled at 'guilefulness' that guilds actually developed strict codes to prevent members from deceiving each other—showing how dangerous unchecked trickery was considered in commerce.
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