Unfavourable publicity given to metrical composition (7)
I believe the answer is:
adverse
'unfavourable' is the definition.
(similar in meaning)
'publicity given to metrical composition' is the wordplay.
'publicity' becomes 'ad' (short for advert).
'given to' says to put letters next to each other.
'metrical composition' becomes 'verse' (I can't explain this - if you can you should give a lot more credence to this answer).
'ad'+'verse'='ADVERSE'
Can you help me to learn more?
(Other definitions for adverse that I've seen before include "Opposed to or unfavourable" , "Dire" , "Hostile" , "Detrimental" , "Contrary -- inauspicious" .)