Hard-hearted (8)
'hardhearted' is the definition.
(similar in meaning)
This is all the clue.
(Other definitions for obdurate that I've seen before include "Obstinate and unrepentant" , "hard to influence" , "Inflexible" , "A doubter being stubborn" , "Stiff-necked" .)
'hard-hearted' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for ruthless that I've seen before include "Unmerciful" , "Without mercy or pity" , "Unsparing" , "Without pity or compassion" , "Hard-hearted" .)