Possibly relating to the whole? (8)
I believe the answer is:
integral
'the whole' is the definition.
(I've seen this before)
'possibly relating' is the wordplay.
'possibly' indicates an anagram.
'relating' with letters rearranged gives 'INTEGRAL'.
'to' is the link.
(Other definitions for integral that I've seen before include "Formed of constituent parts" , "Inbuilt, essential" , "though whole" , "Of part necessary to the completeness of a whole" , "Forming an essential part" .)