Judge, say, goes north round part of the summer (5)
I believe the answer is:
gauge
'judge' is the definition.
(I know that judge can be written as gauge)
'say goes north round part of the summer' is the wordplay.
'say' becomes 'eg' (both can mean 'for example').
'goes north' says the letters should be written in reverse (I've seen 'going north' mean this).
'round' indicates putting letters inside.
'part of the summer' becomes 'Aug' ('Aug' is part of 'summer').
'eg' written backwards gives 'ge'.
'ge' going around 'aug' is 'GAUGE'.
(Other definitions for gauge that I've seen before include "Meter" , "Measure - estimate" , "Distance between the rails of a railway track" , "Judge" , "Instrument to measure or test" .)