On the same side starting for all sides today (4)
I believe the answer is:
with
'on' is the definition.
Both the answer and definition are adverbs. Perhaps there's a link between them I don't understand?
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for with that I've seen before include "See 5" , "In the presence of" , "Characterised by" , "By means of" , "In spite of" .)