__ in a blue moon (rarely) (4)

I believe the answer is:

once

(Other definitions for once that I've seen before include "Quick examination" , "in bygone days" , "On a single (or past) occasion" , "Long ago" , "One-time musical film and song" .)

I've seen this clue in the Newsday.

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.