Nut for poor old man (6)
I believe the answer is:
almond
'nut' is the definition.
(almond is a type of nut)
'poor old man' is the wordplay.
'poor' indicates an anagram.
'old'+'man'='oldman'
'oldman' with letters rearranged gives 'ALMOND'.
'for' is the link.
(Other definitions for almond that I've seen before include "Oval-shaped nut" , "Marzipan-producing nut" , "Fruit for marzipan" , "Old man (anag)" , "Fruit kernel of a peach-related tree" .)