Hired assassin decapitated poet (3,3)
I believe the answer is:
hit man
'hired assassin' is the definition.
(I've seen this before)
'decapitated poet' is the wordplay.
'decapitated' means to remove the first letter.
'poet' becomes 'Whitman' (19th-century American poet Walt Whitman).
'whitman' with its initial letter removed is 'HIT-MAN'.
(Other definitions for hit man that I've seen before include "Hired killer" , "Hired murderer" , "A modern hired assassin" , "One killing" , "Modern description of assassin" .)