Reel for thread (6)
I believe the answer is:
bobbin
'reel for thread' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for bobbin that I've seen before include "Reel, spool" , "about which a yarn is spun" , "Cylinder for winding thread" , "Reel for yarn" , "Cotton reel" .)