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Webster 1913 Edition

Noun.

The quality or state of being dumb; muteness; silence; inability to speak.

Noun.

Dumness.

Muteness; silence or holding the peace; omission of speech. This is voluntary dumbness.

In capacity to speak; inability to articulate sounds. This is involuntary dumbness.

dumbness ‎(usually uncountable, plural dumbnesses)

The state of being dumb or mute: that is, of not communicating vocally, whether from selective mutism (refusal to speak) or from an inability to speak.
- 1944, Emily Carr, The House of All Sorts, "Sissy's Job,"
  He was a deaf-mute. His dumbness did not seem to matter when we were boys.
Muteness, silence; abstention from speech.
- 1611 Shakespeare, William [first known show: 15 May 1611; posthumous publication: 1623], Winter's Tale, Act 5, Scene 2:
  There was speech in their dumbness.
Show or gesture without words; pantomime; dumb-show.
- 1623 Shakespeare, William [posthumous publication], Timon of Athens, Act 1, Scene 1:
  To the dumbness of the gesture one might interpret.
(informal) The quality of being stupid or foolish.

the state of being dumb