Asian king's quiet sound of realisation (4)
I believe the answer is:
shah
'asian king's' is the definition.
'shah' can be an answer for 'king's' (I have seen 'King of Persia' mean 'shah' so perhaps 'king' could also mean 'shah'). I am unsure of the 'asian' bit.
'quiet sound of realisation' is the wordplay.
'quiet' becomes 'sh' ('sh' is used to tell someone to be quiet).
'sound of realisation' becomes 'ah' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'sh'+'ah'='SHAH'
Can you help me to learn more?
(Other definitions for shah that I've seen before include "Persian emperor" , "Sovereign ousted in 1979" , "Emperor of Iran" , "Former ruler of Persia" , "King of Persia" .)