Second downgrade is reasonable (8)
I believe the answer is:
moderate
'reasonable' is the definition.
(similar in meaning)
'second downgrade' is the wordplay.
'second' becomes 'mo' (both are short periods of time).
'downgrade' becomes 'derate' (I can't explain this - if you can you should believe this answer much more).
'mo'+'derate'='MODERATE'
'is' is the link.
Can you help me to learn more?
(Other definitions for moderate that I've seen before include "Chair" , "Medium in amount or intensity" , "Within reasonable or average limits" , "Average; make less extreme" , "Lessen the intensity" .)