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 advertisement).
'given to' means one lot of letters go next to another.
'metrical composition' becomes 'verse' (I am not sure about this - if you are sure you should believe this answer much more).
'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" .)