Not the first worker to be used (6,4)
I believe the answer is:
second hand
'be used' is the definition.
(I've seen this before)
'not the first worker' is the wordplay.
'not the first' becomes 'second' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'worker' becomes 'hand' (hand is a kind of worker).
'second'+'hand'='SECOND-HAND'
'to' is the link.
Can you help me to learn more?
(Other definitions for second hand that I've seen before include "not original" , "Watch component" , "Previously owned - part of watch" , "being employed again" , "Pre-owned - used" .)