Material needed by witness at inquest (5)
I believe the answer is:
satin
'material' is the definition.
(I know that satin is a type of material)
'needed by witness at inquest' is the wordplay.
'needed by' indicates the answer is hidden within the clue (the solution letters are needed to write the clue).
'SATIN' is hidden within 'witness at inquest'.
(Other definitions for satin that I've seen before include "Stain on shiny cloth" , "Silk fabric" , "Material with glossy front and dull back" , "Saint (anag.)" , "Glossy textile" .)