The dog is more determined (6)
I believe the answer is:
setter
I believe this is a double definition.
'the dog' is the first definition.
(setter is a type of dog)
'more determined' is the second definition.
('set' can be a synonym of 'determined')
'is' acts as a link.
(Other definitions for setter that I've seen before include "Bird trained to scent game" , "Puzzle creator" , "Thematic type [DOG]" , "One barking" , "stream of cattle" .)