Definition: acuteness of mental discernment and soundness of judgment

Origin: Sagacity can be traced to the Latin sagācitās meaning “wisdom.” It entered English in the mid-1500s.

Example: “Never before that night had I felt the extent of my own powers–of my sagacity. I could scarcely contain my feelings of triumph. To think that there I was, opening the door, little by little, and he not even to dream of my secret deeds or thoughts.”
Edgar Allan Poe, “The Tell-Tale Heart,” The Pioneer, January, 1843