Fears are unnatural to old sailor (8)
I believe the answer is:
seafarer
'old sailor' is the definition.
'seafarer' can be an answer for 'sailor' (seafarer is a kind of sailor). I'm unsure of the 'old' bit.
'fears are unnatural' is the wordplay.
'unnatural' is an anagram indicator.
'fears'+'are'='fearsare'
'fearsare' anagrammed gives 'SEAFARER'.
'to' acts as a link.
Can you help me to learn more?
(Other definitions for seafarer that I've seen before include "Traveller by ship" , "One going by ship" , "'Mariner, sailor (8)'" , "Jack" , "Rating maybe" .)