Italian speaking in a whisper (5,4)

I believe the answer is:

sotto voce

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'in a whisper' is the definition.
(thesaurus)

I can't explain the rest of the clue.

(Other definitions for sotto voce that I've seen before include "Like subdued talking" , "on the quiet" , "Spoken quietly" , "Speaking quietly" , "In an undertone, from Italian" .)

I've seen this clue in The Guardian.

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