Old duke in Scottish river now (5)
I believe the answer is:
today
'now' is the definition.
(synonyms)
'old duke in scottish river' is the wordplay.
'old' becomes 'o' (abbreviation).
'duke' becomes 'd' (abbreviation).
'in' indicates putting letters inside.
'scottish river' becomes 'tay' (the River Tay in Scotland).
'o'+'d'='od'
'od' placed into 'tay' is 'TODAY'.
(Other definitions for today that I've seen before include "one of our papers, once" , "Presently" , "At the present time, in general" , "Yesterday's tomorrow" , "The present time or age" .)