Rising European politician adopts old literary form (4)
I believe the answer is:
poem
'literary form' is the definition.
(I know that poem is a literary form)
'rising european politician adopts old' is the wordplay.
'rising' is a reversal indicator (in a down clue, letters go up).
'european politician' becomes 'MEP' (Member of European Parliament).
'adopts' is an insertion indicator.
'old' becomes 'o' (abbreviation as in OT - Old Testament).
'mep' placed around 'o' is 'meop'.
'meop' back-to-front is 'POEM'.
(Other definitions for poem that I've seen before include "Verse form" , "Mope about in verse" , "Literary composition, sometimes in verse" , "Rhyme" , "Ode" .)