Length of hair (5)
I believe the answer is:
tress
'length of hair' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for tress that I've seen before include "is a bit of a shock" , "Curl - lock" , "Long lock or plait of hair" , "Obsolete support" , "Long piece of hair" .)