The word "sly" describes someone who is cunning, stealthy, or clever in a deceptive way. A sly person often uses trickery or deceit to achieve their goals, and they may act in a way that is not straightforward or honest. This word often carries a negative connotation, suggesting that the person may be untrustworthy or manipulative.
The term "sly" originates from the Middle English word "sly", which comes from the Old Norse word "slyrr", meaning "sly, crafty". The word has evolved through the centuries while retaining its core meaning related to cleverness and deceit.