Some blackguard entirely zealous (6)

I believe the answer is:

ardent

'zealous' is the definition.
(synonyms)

'some blackguard entirely' is the wordplay.
'some' says the answer is hidden in the clue (some of the parts of the word are used).
'ARDENT' is hidden in the letters of 'blackguard entirely'.

(Other definitions for ardent that I've seen before include "Zealous - ranted (anag)" , "Enthusiastic or passionate" , "Intensely devoted" , "very interested" , "Warm and loving" .)

I've seen this clue in The Sun.

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.