Relentless golfer is on eighteenth at last (8)
I believe the answer is:
tigerish
'relentless' is the definition.
Both the definition and answer are adjectives. Maybe you can see a link between them that I can't see?
'golfer is on eighteenth at last' is the wordplay.
'golfer' becomes 'Tiger' (US golfer Tiger Woods).
'on' says to put letters next to each other.
'at last' suggests the final letters.
The last letter of 'eighteenth' is 'h'.
'tiger'+'is'+'h'='TIGERISH'
Can you help me to learn more?
(Other definitions for tigerish that I've seen before include "Fierce" , "feistiness" .)