From son to father (6)
I believe the answer is:
filial
'from son to father' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for filial that I've seen before include "Appropriate to issue" , "Of or due from son or daughter, perhaps affection" , "Dutiful like son or daughter" , "Relating to sons or daughters" , "Proper to a son or daughter" .)