Small envelope (6)
I believe the answer is:
sachet
'small envelope' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for sachet that I've seen before include "Small bag or sealed plastic pack" , "Small packet (of, eg, shampoo)" , "Chaste as a sealed plastic bag" , "Small sealed packet" , "Small bag with sweet-smelling substance" .)