Fastening ship’s first staff (5)
I believe the answer is:
screw
'fastening' is the definition.
(I know that screw is a type of fastening)
'ship's first staff' is the wordplay.
'ship's first' becomes 's' (1st letter of 'ship').
'staff' becomes 'crew' (crew of workers).
's'+'crew'='SCREW'
(Other definitions for screw that I've seen before include "Prison officer (slang)" , "Propeller; fixing pin" , "The Turn of the ___ , 1898 Henry James horror story" , "Fastener; propeller" , "Fixer needing driver" .)