Sound made by duck for princess in opera? (3)
I believe the answer is:
ida
'princess in opera?' is the definition.
(Princess Ida is a Gilbert and Sullivan opera)
'sound made by duck' is the wordplay.
'sound made by' indicates a 'sounds like' (homophone) clue.
'duck' becomes 'eider duck' (eider is a type of duck).
'eider' is a homophone of 'IDA'.
'for' is the link.
(Other definitions for ida that I've seen before include "The girl for Dai" , "Greek mount - Gilbertian princess" , "musical princess" , "Poetic princess" , "- Rubinstein, Russian dancer, actress" .)