The ironic term for a perceptive person sherlock is first seen in print in 1903, naturally named after fictional detective Sherlock Holmes. His full name had been used in this way since 1896 (e.g. “you’re a regular Sherlock Holmes”), an impressive rise considering he first appeared in 1887.

Being given a rare first name likely contributed to this eponym’s popularity. Sherlock is originally an uncommon English last name, which have rarely gotten used as first names since last names were first instituted. It’s the blond version of Blacklock, Silverlock, or Harlock (har meaning “grey” in Old English; the Modern English equivalent is hoar), where scir is another Old English color term meaning “bright” (Modern English sheer) that has fallen out of use.