Run-down theatre has it after December (8)
I believe the answer is:
decrepit
'run-down' is the definition.
(I've seen this before)
'theatre has it after december' is the wordplay.
'theatre' becomes 'rep' (I've seen this in other clues**).
'has' says to put letters next to each other.
'after' says to put letters next to each other.
'december' becomes 'dec' ('Dec' can be a synonym of 'december').
'rep' next to 'it' is 'repit'.
'repit' put after 'dec' is 'DECREPIT'.
(Other definitions for decrepit that I've seen before include "Dilapidated, made weak by age" , "run down" , "Getting on" , "Feeble - dilapidated" , "Worn and broken down by use" .)