Visit source of Scottish river (4)
I believe the answer is:
stay
'visit' is the definition.
(thesaurus)
'source of scottish river' is the wordplay.
'source of' suggests taking the first letters.
'river' becomes 'tay' (Scottish river**).
The first letter of 'scottish' is 's'.
's'+'tay'='STAY'
(Other definitions for stay that I've seen before include "Remain; steady" , "guy to > put off" , "Rope or wire used to support a mast" , "Remain; detain" , "Arrest" .)