Break in spring in lock (8)
I believe the answer is:
trespass
'break in' is the definition.
(thesaurus)
'spring in lock' is the wordplay.
'spring' becomes 'spa' (I've seen this before).
'in' means one lot of letters goes inside another.
'lock' becomes 'tress' (I've seen this before).
'spa' inserted into 'tress' is 'TRESPASS'.
(Other definitions for trespass that I've seen before include "Enter someone else's property illegally" , "Enter another's property unlawfully" , "Enter land illegally" , "Illegal entry" , "Enter the Forbidden Land" .)