Your setter’s in good nick for a start: that’s specified (5)
I believe the answer is:
given
'specified' is the definition.
(similar in meaning)
'your setter's in good nick for a start' is the wordplay.
'your setter' becomes 'ive' (I can't explain this - if you can you should give a lot more credence to this answer).
'in' is an insertion indicator.
'for a start' suggests taking the first letters.
The initial letters of 'good nick' is 'gn'.
'ive' placed inside 'gn' is 'GIVEN'.
'that's' is the link.
Can you help me to learn more?
(Other definitions for given that I've seen before include "Provided" , "Bestowed" , "Handed over; an 18 dn" , "Taken as read" , "assumed fact" .)