What fastens and unfastens locks? (7)
I believe the answer is:
hairpin
'what fastens and unfastens locks?' is the definition.
I know that 'locks' relates to this answer.
'and unfastens locks?' is the wordplay.
I cannot really understand how this works, but
'and' could be 'n' (common abbreviation for 'and') and 'n' is located in the answer.
'locks?' could be 'hair' (I've seen this before) and 'hair' is present in the answer.
The remaining letters 'pi' is a valid word which might be clued in a way I don't understand.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for hairpin that I've seen before include "Very sharp bend in mountain road" , "grip?" , "Device for fastening one's locks" , "Bit of metal" , "Fastener for tresses" .)