Don's swimming in a river among other things (3,2,5)
I believe the answer is:
and so forth
'among other things' is the definition.
Both the definition and answer are adverbs. Perhaps you can see an association between them that I don't see?
'don's swimming in a river' is the wordplay.
'swimming' indicates anagramming the letters.
'in' is an insertion indicator.
'river' becomes 'forth' (Scottish river).
'dons' with letters rearranged gives 'ndso'.
'a'+'forth'='aforth'
'ndso' inserted within 'aforth' is 'AND SO FORTH'.
Can you help me to learn more?
(Other definitions for and so forth that I've seen before include "Et cetera" , "implies others of the same type" , "etc." , "Along with other things" , "imagine what follows" .)