Stop located on the right side — not something unknown (5)
I believe the answer is:
deter
'stop' is the definition.
(I've seen this before)
'on the right side not something unknown' is the wordplay.
'on' indicates putting letters inside (as in clothing \'on\' a person).
'the right side' means to take half the letters.
'not' becomes 'nt' (synonyms).
'something unknown' becomes 'deer' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'nt' halved is 't'.
't' placed into 'deer' is 'DETER'.
'located' acts as a link.
This may not be correct. It may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for deter that I've seen before include "Discourage or impede" , "Cause not to do something" , "Discourage or prevent from doing something" , "Daunt" , "Warn off" .)