Lock with a spring in it? (7)
I believe the answer is:
ringlet
'lock' is the definition.
(both can mean a piece of someone's hair)
'spring in it?' is the wordplay.
I cannot really understand how this works, but
'in' is within the answer.
'it?' could be 't' (abbreviation. e.g. in 'tis) and 't' is found in the answer.
This explanation may well be incorrect...
'with a' is the link.
Can you help me to learn more?
(Other definitions for ringlet that I've seen before include "Long curl of hair" , "Hair feature" , "Curling lock of hair" , "Bit of hair" , "Curl or tendril" .)