underbreath

underbreath

(ˈʌndəˌbrɛθ)
n
a whisper
adj
hushed or whispered
adv
in a hushed manner
References in classic literature ?
"What--after all--my insulting slap, too!" said she in an underbreath. She was so utterly exhausted that she had not strength to speak louder.
C We sat in class & laughed, carried on underbreath, looked at all the pretty girls.