Respectable clothing in the current era is in decline (8)
I believe the answer is:
decadent
'in decline' is the definition.
(I've seen this before)
'respectable clothing in the current era' is the wordplay.
'respectable' becomes 'decent' (similar in meaning).
'clothing' indicates putting letters inside (some letters cover up or clothe others).
'in the current era' becomes 'AD' (AD, Anno Domini, as opposed to BC, Before Christ).
'decent' placed around 'ad' is 'DECADENT'.
'is' is the link.
(Other definitions for decadent that I've seen before include "Decanted in corrupt way" , "Reflecting a state of moral decline" , "Marked by excessive self-indulgence and moral decay" , "Abandoning principles" , "Morally corrupt" .)