monotone

noun
  1. 1

    A single unvaried tone of speech or a sound.

    โ€œWhen Tima felt like her parents were treating her like a servant, she would speak in monotone and act as though she were a robot.โ€

  2. 2

    A piece of writing in one strain throughout.

verb
  1. 1

    To speak in a monotone.

adjective
  1. 1

    (of speech or a sound) Having a single unvaried pitch.

  2. 2

    Being, or having the salient properties of, a monotone function.

    โ€œThe function f(x):=x^3 is monotone on \R, while g(x):=x^2 is not.โ€

Source: https://en.wiktionary.org/wiki/monotone