Picked up suitable one to wear fancy raincoat for approval (12)
I believe the answer is:
ratification
'for approval' is the definition.
(ratification is a kind of approval)
'picked up suitable one to wear fancy raincoat' is the wordplay.
'picked up' says the letters should be written backwards.
'suitable' becomes 'fit' (similar in meaning).
'one' becomes 'i' (Roman numeral).
'to wear' indicates putting letters inside (to wear something is to be covered up by it).
'fancy' indicates an anagram.
'fit' reversed gives 'tif'.
'tif'+'i'='tifi'
'raincoat' with letters rearranged gives 'racation'.
'tifi' put within 'racation' is 'RATIFICATION'.
(Another definition for ratification that I've seen is " Process of making a treaty official".)