US prosecutor needs to disguise material (6)
I believe the answer is:
damask
'material' is the definition.
(I know that damask is a type of material)
'us prosecutor needs to disguise' is the wordplay.
'us prosecutor' becomes 'DA' (district attorney).
'needs' says to put letters next to each other.
'to disguise' becomes 'mask' (masking is a kind of disguising).
'da'+'mask'='DAMASK'
(Other definitions for damask that I've seen before include "Silk or linen material woven with pattern on either side" , "Figured material" , "Reversible fabric - type of rose" , "Lustrous fabric" , "Table linen material" .)