Unfavourable notice on poem (7)
I believe the answer is:
adverse
'unfavourable' is the definition.
('adverse' can be similar in meaning to 'unfavourable')
'notice on poem' is the wordplay.
'notice' becomes 'ad'.
'on' means one lot of letters go next to another.
'poem' becomes 'verse' (verse is a kind of poem).
'ad'+'verse'='ADVERSE'
(Other definitions for adverse that I've seen before include "Unfavourable or harmful, perhaps criticism" , "Unfavourable of the week" , "Dire" , "Unfavourable to evaders" , "Contrary, harmful" .)