Source : Webster's Revised Unabridged Dictionary (1913)

Mussitation \Mus`si*ta"tion\, n. [L. mussitatio suppression of
   the voice, fr. mussitare to be silent, to murmur.]
   A speaking in a low tone; mumbling. [Obs.]

Source : WordNet®

mussitation
     n : a low continuous indistinct sound; often accompanied by
         movement of the lips without the production of articulate
         speech [syn: {mutter}, {muttering}, {murmur}, {murmuring},
          {murmuration}]