So Cretan possibly is forefather (8)
I believe the answer is:
ancestor
'is forefather' is the definition.
(I've seen this before)
'so cretan possibly' is the wordplay.
'possibly' indicates anagramming the letters.
'so'+'cretan'='socretan'
'socretan' with letters rearranged gives 'ANCESTOR'.
(Other definitions for ancestor that I've seen before include "one is up a tree" , "Person from whom one is descended" , "One of one's forebears" , "Forefather" , "Adam was our first one" .)