An elastic band (6)
I believe the answer is:
garter
'an elastic band' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for garter that I've seen before include "- Belt; - snake; - stitch" , "Band involved in hold-up" , "Band to hold up a stocking" , "Band to keep a stocking or sleeve up" , "Sock supporter" .)