Yarn unit (5)
I believe the answer is:
skein
'yarn unit' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for skein that I've seen before include "Hank" , "Loosely coiled length of thread" , "Loose bundle of yarn" , "Coiled length of yarn" , "Flock of flying geese" .)