Have to defend English poet (4)
I believe the answer is:
owen
'poet' is the definition.
(I've seen this before)
'have to defend english' is the wordplay.
'have' becomes 'own' (synonyms).
'to defend' is an insertion indicator.
'english' becomes 'e' (abbreviation).
'own' placed around 'e' is 'OWEN'.
(Other definitions for owen that I've seen before include "English war poet, killed 1918" , "'E won over the Welshman" , "Welsh boy's name" , "Wilfred - - , WWI poet" , "Welsh industrialist and social reformer, founder of cooperative communities, d. 1858" .)