Small Scottish river? Check (4)
I believe the answer is:
stay
'check' is the definition.
(staying is a kind of checking)
'small scottish river?' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'scottish river?' becomes 'tay' (I've seen this before**).
's'+'tay'='STAY'
(Other definitions for stay that I've seen before include "Remain; detain" , "Corset strut" , "Remain; suspend" , "Supporter" , "Remain behind" .)