Greenish-yellow liqueur made from a secret formula developed at a monastery at Fecamp in France in about 1510 (11)

I believe the answer is:

benedictine

(Other definitions for benedictine that I've seen before include "Monk - nun - liqueur" , "Ampleforth, Downside order of monks" , "Brother" , "Religious" , "drink" .)

I've seen this clue in The Independent.

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.