Silentness.
Noiseless; still; unspoken; not speaking; mute.
She was silent for a moment. – Man and Maid by Elinor Glyn
But why so silent? – Tales From the 'Phantasus', etc. of Ludwig Tieck by Ludwig Tieck
Why are you silent, Pelagea Ivanovna? – The Wife and Other Stories by Anton Chekhov