Stressed about lock (5)
I believe the answer is:
tress
'lock' is the definition.
(both can mean a piece of hair)
'stressed about' is the wordplay.
'about' indicates a hidden word (the clue goes around or about the answer).
'TRESS' is hidden within 'stressed'.
(Other definitions for tress that I've seen before include "Long lock or plait of hair" , "Braid of hair" , "Switch" , "Rests (anag.)" , "Curl - lock" .)