Of the voice or speech: low, uttered in an undertone, subdued.

Of the voice: low, subdued. Cf. submiss, adj. 2. Now rare.

Of the voice: low, subdued; = submiss, adj. 2.

Of the voice or a sound: Uttered without due opening of the mouth, so as not to be clearly heard; muffled, indistinct. (Cf. ‘to speak out’.) Also…

As adj. Uttered, etc., in an undertone.

expressed in an undertone.

Of a word, speech, etc.: that is uttered so as to be barely audible, murmured; (also) formed in one's mind without being uttered or spoken aloud. Cf…