Sheath for a sword (8)
I believe the answer is:
scabbard
'sheath for a sword' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for scabbard that I've seen before include "Something to stick the knife into" , "Holding a weapon" , "Case for a sword" , "Holder for a bladed weapon" , "One holding a sword" .)