Back in a cell, utterly reject fine material (5)
I believe the answer is:
tulle
'fine material' is the definition.
(I've seen this before)
'back in a cell utterly reject' is the wordplay.
'back' says the letters should be written in reverse.
'in' says the answer is hidden in the clue.
'ellut' is hidden within 'cell utterly reject'.
'ellut' written backwards gives 'TULLE'.
(Other definitions for tulle that I've seen before include "Thin material" , "Delicate netted fabric" , "Fine net material" , "Silk net fabric" , "French town" .)