toneless

tone +‎ -less

toneless (comparative more toneless, superlative most toneless)

1. Lacking tone or expression.
   • 1928, Radclyffe Hall, The Well of Loneliness, Chapter 7,

     And sure enough she had settled down at once, so that in less than two months it seemed to Stephen that Miss Puddleton must always have been at Morton, must always have been sitting at the large walnut table, must always have been saying in that dry, toneless voice with the Oxford accent: ‘You’ve forgotten something, Stephen,’ […]

   • 1941, Emily Carr, Klee Wyck, Chapter 4,

     The Cumshewa totem poles were dark and colourless, the wood toneless from pouring rain.

2. Lacking vitality; listless.
3. (linguistics) Lacking tone or pitch, have the neutral tone.

• tonelessly

• noteless