Military item of clothing? Some fake piece (4)
I believe the answer is:
kepi
'military item of clothing?' is the definition.
(type of hat used by some militaries)
'some fake piece' is the wordplay.
'some' indicates the answer is hidden within the clue (some of the parts of the word are used).
'KEPI' can be found hidden inside 'fake piece'.
(Other definitions for kepi that I've seen before include "French military cap" , "French military hat" , "Service cap" , "French military headgear" , "Flat-topped military cap" .)