A racing event – one on river, say (7)
I believe the answer is:
regatta
'a racing event one on river say' is the definition.
I can't judge whether this definition defines the answer.
'a racing event one on river say' is the wordplay.
'racing event' becomes 'TT' (Isle of Man Tourist Trophy races).
'one' becomes 'a' (a thing is one thing).
'on' means one lot of letters go next to another.
'river' becomes 'r' (abbreviation for river).
'say' becomes 'eg' (short for 'exempli gratia', 'for example' in Latin).
'a'+'tt'+'a'='atta'
'r'+'eg'='reg'
'atta' after 'reg' is 'REGATTA'.
Can you help me to learn more?
(Other definitions for regatta that I've seen before include "Series of yacht races" , "Yachting gala" , "Event for craft" , "Yachting or rowing event" , "Number of yachts in sporting event" .)