Sunak's written about Old English verse (4)
I believe the answer is:
poem
'verse' is the definition.
(I've seen this before)
'sunak's written about old english' is the wordplay.
'sunak' becomes 'pm' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'written about' indicates putting letters inside.
'old english' becomes 'OE'.
'pm' going around 'oe' is 'POEM'.
Can you help me to learn more?
(Other definitions for poem that I've seen before include "Ode" , "Piece of verse" , "Rhyme" , "Eg, If-" , "Literary composition, sometimes in verse" .)