Princess thought English expendable (3)

I believe the answer is:

ida

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'princess' is the definition.
(Princess Ida is a Gilbert and Sullivan opera)

I don't understand the remainder of the clue.

Can you help me to learn more?

(Other definitions for ida that I've seen before include "princess on stage" , "'Princess - - ' (G & S)" , "Cretan mountain - Gilbert and Sullivan princess" , "Cretan mount" , "Stagey princess" .)

I've seen this clue in The Sun.

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