Writer, Gunter, not half impressing international publisher (7)
I believe the answer is:
penguin
'publisher' is the definition.
(Penguin is a publishing house)
'writer gunter not half impressing international' is the wordplay.
'writer' becomes 'pen' (something which writes).
'not half' indicates taking half.
'impressing' indicates putting letters inside (impress historically meant to conscript).
'international' becomes 'i' (abbreviation eg in IMF).
'gunter' cut in half is 'gun'.
'gun' going around 'i' is 'guin'.
'pen'+'guin'='PENGUIN'
(Other definitions for penguin that I've seen before include "Black-and-white antarctic bird" , "King or emperor?" , "paperback" , "Antarctic seabird with flippers for wings" , "Chocolate biscuit" .)