Officer material with barnet oddly cut (8)
I believe the answer is:
sergeant
'officer' is the definition.
(sergeant is a kind of officer)
'material with barnet oddly cut' is the wordplay.
'material' becomes 'serge' (serge is a kind of material).
'with' is a charade indicator (letters next to each other).
'oddly cut' indicates alternate letters (letters in odd-numbered positions removed).
The alternate letters of 'barnet' are 'ant'.
'serge'+'ant'='SERGEANT'
(Other definitions for sergeant that I've seen before include "Troy" , "one with stripes" , "Man in charge" , "Reagents for army NCO" , "NCO; Death a fell one, Hamlet" .)