Thickset powerful dog (7)

I believe the answer is:

mastiff

(Other definitions for mastiff that I've seen before include "Powerful breed of watchdog" , "Powerful dog breed" , "one of his best friends?" , "Powerful, smooth-coated dog used for security work" , "Strong breed of dog" .)

I've seen this clue in The Telegraph.

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.