Makes marginal movement sideways (5)
I believe the answer is:
edges
'makes' is the definition.
The answer and definition can be both to do with motion as well as being verbs in their -s form.
Perhaps they are linked in a way I don't understand?
'marginal movement sideways' is the wordplay.
'marginal' becomes 'edge' (synonyms).
'movement sideways' becomes 's' (I can't justify this - if you can you should give a lot more credence to this answer).
'edge'+'s'='EDGES'
Can you help me to learn more?
(Other definitions for edges that I've seen before include "They're used for cutting" , "They're farthest from the middle" , "Margins" , "Borders, rims" , "Slowly moves" .)