Nan told wimp off for hoax with skull (8,3)
I believe the answer is:
piltdown man
'hoax with skull' is the definition.
(paleoanthropological hoax)
'nan told wimp off' is the wordplay.
'off' is an anagram indicator.
'nan'+'told'+'wimp'='nantoldwimp'
'nantoldwimp' with letters rearranged gives 'PILTDOWN MAN'.
'for' is the link.
(Other definitions for piltdown man that I've seen before include "1912 Sussex fossil hoax - not limp wand (anag)" , "Hoax purporting to be fossil hominid" , "forgery" , "[HOAX] - with 7a" , "Pithecanthropus Dawsonii" .)