Ground-breaking (13)

I think it could be either:

revolutionary

unprecedented

(Other definitions for revolutionary that I've seen before include "Insurgent - involving dramatic change" , "Causing dramatic change" , "Innovative" , "New" , "French calendar?" .)

I've seen this clue in The Guardian, The Times and The Sunday 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.