Very secretive sort (6)

I believe the answer is:

enigma

(Other definitions for enigma that I've seen before include "Mysterious person" , "Mysteriously puzzling person or thing" , "cryptic puzzle!" , "Solution to mystery" , "German military cipher machine" .)

I've seen this clue in The New York Times.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.