up to no good
Doing something mischievous or wrong
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Main Entry: ↑good
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doing or planning something bad, illegal, or immoral
Thesaurus: morally bad or wrongsynonym
Main entry: good
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doing something wrong
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up to no good
informal : doing bad things or planning to do bad things
If you ask me, that woman's up to no good.
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Main Entry: ↑good
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up to no ˈgood idiom
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Those kids are always up to no good.
Useful english dictionary. 2012.