a person who tries to find an explanation for a crime or something mysterious, or who shows that they understand something quickly, especially something that is not obviousOh, well done, Sherlock. Did you figure that out all by yourself?Look, I'm no Sherlock Holmes, but I think I know who wrote that letter.From Sherlock Holmes, a very clever detective in stories by Arthur Conan Doyle, published in the late 19th and early 20th centuries.