Failing of trendy company (6)
I believe the answer is:
infirm
'failing' is the definition.
(thesaurus)
'trendy company' is the wordplay.
'trendy' becomes 'in' ('in' can mean fashionable).
'company' becomes 'firm' (firm can mean a company or business).
'in'+'firm'='INFIRM'
'of' acts as a link.
(Other definitions for infirm that I've seen before include "Debilitated" , "Not physically strong" , "not so healthy" , "Feeble from age" , "Sickly" .)