What's the "een" in Halloween?
a clever and perceptive person
That teenager is quite the sherlock.
masc. proper name, literally "fair-haired," from Old English scir "bright" + locc "lock of hair." Slang for "private detective, perceptive person" (the latter often ironic) is attested from 1903, from A.C. Doyle's fictional character Sherlock Holmes (full name in this sense used from 1896; Holmes debuted in 1887 and was popular by 1892).
A clever and perceptive person • Often sarcastic: no shit, Sherlock