In a clever and cunning way, often involving deception or trickery.
From 'crafty' plus the adverbial suffix '-ly,' which converts adjectives to adverbs. The suffix dates back to Old English '-lice' (in the manner of).
Notice how '-ly' adverbs often add a disapproving tone—'he spoke craftily' sounds suspicious in ways that 'he spoke skillfully' doesn't, even though they share the same root word.
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