Mainly greeting a very successful Olympian? (4)
I believe the answer is:
ahoy
'mainly greeting' is the definition.
'ahoy' can be an answer for 'greeting' (I have seen 'Nautical greeting' mean 'ahoy' so perhaps 'greeting' could also mean 'ahoy'). I'm not certain of the 'mainly' bit.
'a very successful olympian?' is the wordplay.
'very successful olympian?' becomes 'hoy' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'a'+'hoy'='AHOY'
Can you help me to learn more?
(Other definitions for ahoy that I've seen before include "A sailor's call to a ship" , "Call for attention at sea" , "Coastal land" , "Mariner's call" , "Sailor's greeting" .)