Keyless lock (5)
I believe the answer is:
tress
'keyless lock' is the definition.
'tress' can be an answer for 'lock' (both can mean a piece of hair). I'm not certain of the 'keyless' bit.
'keyless lock' is the wordplay.
'keyless' becomes 't' (I can't explain this - if you can you should give a lot more credence to this answer).
'lock' becomes 'ress' (I've seen this in another clue).
't'+'ress'='TRESS'
Can you help me to learn more?
(Other definitions for tress that I've seen before include "Curl - lock" , "Long lock or plait of hair" , "Long piece of hair" , "Switch" , "Rests (anag.)" .)