Commercial poetry is unfavourable (7)
I believe the answer is:
adverse
'unfavourable' is the definition.
(similar in meaning)
'commercial poetry' is the wordplay.
'commercial' becomes 'ad' (abbreviation for advertisement).
'poetry' becomes 'verse' (lines written in verse).
'ad'+'verse'='ADVERSE'
'is' is the link.
(Other definitions for adverse that I've seen before include "Inopportune" , "Unfavourable - red vase (anag)" , "Unfavourable to evaders" , "Conflicting" , "negative result" .)