Lower parts I learned once with European soprano transposed upwards (7)

I believe the answer is:

secondi

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'lower parts' is the definition.
(I've seen this before)

I can't explain the remainder of the clue.

(Other definitions for secondi that I've seen before include "Parts of duet" , "Lower parts" , "Bass parts" .)

I've seen this clue in The Sunday Times and The Times.

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