Missing the start, emphasise lock (5)
I believe the answer is:
tress
'lock' is the definition.
(both can mean a piece of hair)
'missing the start emphasise' is the wordplay.
'missing the start' means to remove the first letter.
'emphasise' becomes 'stress' (synonyms).
'stress' with its initial letter removed is 'TRESS'.
(Other definitions for tress that I've seen before include "Curl - lock" , "Long piece of hair" , "Long lock or plait of hair" , "Rests (anag.)" , "is a bit of a shock" .)