Having the nature or quality of a devil; devilish or wickedly mischievous.
From devil with the adjectival suffix -y (from Old English '-ig'). This productive suffix transforms nouns into adjectives, as seen in 'happy,' 'cloudy,' and 'sleepy.'
The suffix '-y' is one of English's most ancient and productive tools—it can attach to almost any noun to create an adjective ('sky,' 'dreamy,' 'creepy'), making 'devily' a natural formation even if less common than 'devilish.'
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