Art gallery in favour of framing poster, say (5)
I believe the answer is:
prado
'art gallery' is the definition.
'prado' can be an answer for 'gallery' (I've seen this before). I am unsure of the 'art' bit.
'in favour of framing poster say' is the wordplay.
'in favour of' becomes 'pro' (being pro a particular cause).
'framing' means one lot of letters goes inside another (inserted letters are framed by the outside letters).
'poster say' becomes 'ad' (a poster might be an advertisement).
'pro' enclosing 'ad' is 'PRADO'.
Can you help me to learn more?
(Other definitions for prado that I've seen before include "gallery for paintings" , "gallery abroad" , "picture-house" , "Madrid museum" , "exhibits here?" .)