Stored in pocket, a long optical device (6)
I believe the answer is:
etalon
(Other definitions for etalon that I've seen before include "Spectroscopic device" , "measuring instrument" , "Reflecting device producing interfering light beams" .)
I've seen this clue in The 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.