Officer material with a neat exterior (8)
I believe the answer is:
sergeant
'officer' is the definition.
(sergeant is a kind of officer)
'material with a neat exterior' is the wordplay.
'material' becomes 'serge' (serge is a kind of material**).
'with' says to put letters next to each other.
'exterior' suggests removing the centre.
'neat' with its middle taken out is 'nt'.
'serge'+'a'+'nt'='SERGEANT'
(Other definitions for sergeant that I've seen before include "Estrange (anag)" , "military man" , "Reagents for army NCO" , "NCO or police officer ..." , "Reagents (anag)" .)