Partner; a suffix forming adverbs from adjectives (4)

I believe the answer is:

ally

(Other definitions for ally that I've seen before include "A friendly and reliable country" , "Collaborator, affiliate" , "One co-operating with another" , "Colleague, confederate" , "Confederate; supporter" .)

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