Stop one end, just in case (5)
I believe the answer is:
cease
'stop' is the definition.
(synonyms)
'one end just in case' is the wordplay.
'one end just' becomes 'e' (I can't explain this - if you can you should give a lot more credence to this answer).
'in' means one lot of letters goes inside another.
'e' going inside 'case' is 'CEASE'.
Can you help me to learn more?
(Other definitions for cease that I've seen before include "Discontinue" , "Come to an end" , "Stop, terminate" , "Finish, end" , "Culminate" .)