devilment

Roald Dahlの "The Witches" を読んでいます。
"Where is that grandson of yours?" he said to my grandmother. He spoke rudely and looked very angry.
My grandmother put on her frostiest look, but didn't ansewer him.
"My guess is that he and my son Bruno are up to some devilment," Mr Jenkins went on. "Bruno hasn't turned up for his supper and it takes a lot to make that boy miss his food!"
"devilment" は "devil" から派生した言葉のようですが、辞書で調べます。

・Oxford English Dictionary: Reckless mischief; wild spirits.: his eyes were blazing with devilment

・Collins Dictionary: devilish or mischievous conduct

・Cambridge English Dictionary: behaviour that causes trouble but is usually intended to be humorous: He's up to some kind of devilment again, I'll be bound.
悪ふざけ程度の軽い悪さでしょうか。