Decadent outdoor celebration after revolutionary force cleared out (6)
I believe the answer is:
effete
'decadent' is the definition.
(synonyms)
'outdoor celebration after revolutionary force cleared out' is the wordplay.
'outdoor celebration' becomes 'fete' (as in a church fete).
'after' means one lot of letters go next to another.
'revolutionary' is a reversal indicator.
'cleared out' suggests removing the centre.
'force' with its middle removed is 'fe'.
'fe' reversed gives 'ef'.
'fete' after 'ef' is 'EFFETE'.
(Other definitions for effete that I've seen before include "Over-refined and ineffectual" , "Feeble, lacking vitality" , "Lacking in power" , "Feeble, weak" , "Feeble, having lost vitatlity" .)