Pirate heard ribald melody (7)

I believe the answer is:

corsair

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'pirate' is the definition.
(corsair is a kind of pirate)

'heard ribald melody' is the wordplay.
'heard ribald' becomes 'cors' (I can't justify this - if you can you should believe this answer much more).
'melody' becomes 'air' (air can mean a tune or melody).
'cors'+'air'='CORSAIR'

Can you help me to learn more?

(Other definitions for corsair that I've seen before include "Pirate (archaic)" , "Buccaneer" , "work by Verdi" , "20 across" , "Barbary pirate - pirate ship" .)

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