Crossword Genius

In an undertone (5,4)

Ross

I believe the answer is:

sotto voce

'in an undertone' is the definition.
(I've seen this before)

This is all the clue.

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

I've seen this clue in The Guardian.
Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.