Ancient Scot on river shot (7)
I believe the answer is:
picture
'shot' is the definition.
(thesaurus)
'ancient scot on river' is the wordplay.
'ancient scot' becomes 'pict' (I've seen this before).
'on' means one lot of letters go next to another.
'river' becomes 'ure' (I have seen 'River of Wensleydale ' mean 'ure' so perhaps 'river' could also mean 'ure').
'pict'+'ure'='PICTURE'
(Other definitions for picture that I've seen before include "One can paint a thousand words, it's said" , "Depiction" , "Form a mental image" , "Call to mind" , "Imagine; film" .)