Bank accepting support is failing (8)
I believe the answer is:
moribund
'is failing' is the definition.
(thesaurus)
'bank accepting support' is the wordplay.
'bank' becomes 'mound' (a bank of earth).
'accepting' indicates putting letters inside.
'support' becomes 'rib' (type of architectural support).
'mound' going around 'rib' is 'MORIBUND'.
(Other definitions for moribund that I've seen before include "Not growing or changing" , "At the point of death" , "At death's door" , "Near to death" , "About to die" .)