Speak in an undertone and Speak in hushed tones

Speak in hushed tones and speak in an undertone are semantically related. In some cases you can use "Speak in hushed tones" instead a verb phrase "Speak in an undertone".

Speak in an undertone and speak in hushed tones are semantically related. You can use "Speak in an undertone" instead a verb phrase "Speak in hushed tones".