Third in degree or order (8)

I believe the answer is:

tertiary

(Other definitions for tertiary that I've seen before include "Of the third rank, after secondary" , "very long period" , "Third; period of prehistory" , "Third in order or degree" , "Geological period" .)

I've seen this clue in The Mirror.

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.