Check second Scottish river (4)
I believe the answer is:
stay
'check' is the definition.
(staying is a kind of checking)
'second scottish river' is the wordplay.
'second' becomes 's' (common abbreviation).
'scottish river' becomes 'tay' (I've seen this before**).
's'+'tay'='STAY'
(Other definitions for stay that I've seen before include "Check" , "Wait" , "Stop; support" , "Don't go!" , "hang about" .)