Tiny tree, gnarled for yonks (8)
I believe the answer is:
eternity
'yonks' is the definition.
'tiny tree gnarled' is the wordplay.
'gnarled' is an anagram indicator (gnarled can mean twisted).
'tiny'+'tree'='tinytree'
'tinytree' with letters rearranged gives 'ETERNITY'.
'for' is the link.
(Other definitions for eternity that I've seen before include "Endless period" , "Entirety (anag.)" , "That's a very long time" , "Endless duration" , "Infinite time" .)