A measure is announced for old court sessions (7)
I believe the answer is:
assizes
'court sessions' is the definition.
(I've seen this in another clue)
'a measure is announced for old' is the wordplay.
'measure' becomes 'S' (S is an example).
'is announced for old' becomes 'sizes' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'a'+'s'+'sizes'='ASSIZES'
Can you help me to learn more?
(Other definitions for assizes that I've seen before include "Local courts" , "Former court sessions" , "Old county courts of England" , "Old county court sessions chaired by itinerant judges" , "Old-style county courts" .)