Ruthless brother put pal off at the start (6)
I believe the answer is:
brutal
'ruthless' is the definition.
(thesaurus)
'brother put pal off at the start' is the wordplay.
I cannot quite see how this works, but
'brother' could be 'br' (abbreviation in titles of monks) and 'br' is found in the answer.
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is found in the answer.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for brutal that I've seen before include "Rough and cruel" , "Callous" , "Cruel, heartless" , "Cruel and unfeeling like an animal" , "Cruel, in animal fashion" .)