Opposed to a public notice in poetry (7)
I believe the answer is:
adverse
'opposed' is the definition.
(I've seen this in another clue)
'public notice in poetry' is the wordplay.
'public notice' becomes 'ad' (short for advertisement).
'in poetry' becomes 'verse' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'ad'+'verse'='ADVERSE'
'to a' is the link.
Can you help me to learn more?
(Other definitions for adverse that I've seen before include "Inopportune" , "Unfavourable - red vase (anag)" , "Conflicting" , "'Unfavourable, contrary (7)'" , "Inimical" .)