Sailor's fears are nonsensical (8)
I believe the answer is:
seafarer
'sailor's' is the definition.
(seafarer is a kind of sailor)
'fears are nonsensical' is the wordplay.
'nonsensical' indicates anagramming the letters.
'fears'+'are'='fearsare'
'fearsare' is an anagram of 'SEAFARER'.
(Other definitions for seafarer that I've seen before include "Rating maybe" , "Salt" , "Jack" , "Traveller by ship" , "'Mariner, sailor (8)'" .)