Trendy business does poorly (6)
I believe the answer is:
infirm
'poorly' is the definition.
Both the definition and answer are adjectives. Maybe you can see a link between them that I can't see?
'trendy business' is the wordplay.
'trendy' becomes 'in' ('in' can mean fashionable).
'business' becomes 'firm' (firm is a kind of business).
'in'+'firm'='INFIRM'
'does' acts as a link.
Can you help me to learn more?
(Other definitions for infirm that I've seen before include "Not physically strong" , "Feeble from age" , "Frail" , "Not in good health" , "Feeble, decrepit" .)