* ずるい (zurui): This is probably the closest general equivalent. It implies cunning, shrewdness, and often a slightly negative connotation – like being unfairly clever or deceitful. It's a good choice if "sly" implies trickery or underhandedness.
* 抜け目ない (nukeme nai): This means "not missing anything," "thorough," or "resourceful." It suggests cleverness and attentiveness, often in a positive or neutral light. It's suitable if "sly" implies cleverness and resourcefulness without necessarily being deceitful.
* 狡猾な (kōkatsu na): This word emphasizes cunning and craftiness, often in a negative context. It implies a more deliberate and potentially malicious form of slyness.
* したたか (shitadaka): This describes someone strong-willed, tenacious, and shrewd. It can have positive or negative connotations depending on the context.
To choose the best word, consider the specific context. For example:
* "A sly fox" might be translated as ずるい狐 (zurui kitsune).
* "A sly smile" might be translated as 抜け目ない微笑み (nukeme nai hohoemi) or 狡猾な微笑み (kōkatsu na hohoemi), depending on the intention behind the smile.
Therefore, there's no single answer; the best translation requires understanding the specific meaning and connotation of "sly" in your sentence.