In a devilish, mischievous, or wickedly clever manner; in a way that is playfully naughty or malevolent.
From 'devilish' (adjective) plus '-ly' (from Old English -lice, meaning 'in the manner of'). The '-ly' adverb-forming suffix is one of the most productive in English, turning nearly any adjective into an adverb.
English creates adverbs by adding '-ly' so consistently that we barely notice it—but most languages don't do this. This makes English unique in how easily and predictably we can convert meaning relationships through suffixes.
Complete word intelligence in one call. Free tier — 50 lookups/day.