A river between Central Germany and Switzerland's border (5)
I believe the answer is:
march
'border' is the definition.
(thesaurus)
'a river between central germany and switzerland's' is the wordplay.
'river' becomes 'r'.
'between' is an insertion indicator.
'central' means to look at the middle letters.
'and' is a charade indicator (letters next to each other).
'switzerland' becomes 'ch'.
The middle of 'germany' is 'm'.
'a'+'r'='ar'
'm'+'ch'='mch'
'ar' put within 'mch' is 'MARCH'.
(Other definitions for march that I've seen before include "demo" , "Moving demonstration" , "Walk smartly" , "Month - proceed" , "Walk formally in step with others" .)