Mean state facing decline (7)
I believe the answer is:
average
'mean' is the definition.
(I know that mean can be written as average)
'state facing decline' is the wordplay.
'state' becomes 'aver' (both can mean to declare).
'facing' means one lot of letters go next to another.
'decline' becomes 'age' (get older).
'aver'+'age'='AVERAGE'
(Other definitions for average that I've seen before include "Normal in arithmetic way" , "Mean; standard" , "Arithmetical mean" , "Normal; mean" , "Mean - typical" .)