Ask setter, finally, for puzzle (5)
I believe the answer is:
poser
'puzzle' is the definition.
(I've seen this before)
'ask setter finally' is the wordplay.
'ask' becomes 'pose' (synonyms).
'finally' indicates one should take the final letters.
The last letter of 'setter' is 'r'.
'pose'+'r'='POSER'
'for' is the link.
(Other definitions for poser that I've seen before include "Toughie" , "Pseud" , "Tricky problem" , "Puzzling question for the model" , "Question - a sitter" .)