Adjective

1. having a single unvaried pitch
   • 1799, John Walker, Elements of Elocution, Cooper and Wilson, page 309:

     It is no very difficult matter to be loud in a high tone of voice; but to be loud and forcible in a low tone, requires great practice and management; this, however, may be facilitated by pronouncing forcibly at firſt in a low monotone; a monotone, though in a low key, and without force, is much more ſonorous and audible than when the voice ſlides up and down at almoſt every word, as it muſt do to be various.

   • 1940, Asiatic Society (Calcutta, Royal Asiatic Society of Bengal, India), Journal of the Asiatic Society, page 95:

     The prominence of the syllables is more monotone than in English, the intonation of the latter having a larger variation of stressed and unstressed syllables.

   • 1998, Roger W. Shuy, Bureaucratic Language in Government and Business, Georgetown University Press, Research on Telephone vs. In-Person Administrative Hearings, page 76:

     In the formal register, such variation is reduced and the talk has a more monotone, business-like quality.

1. property of a function to be either decreasing or increasing
   • The function $f(x):=x^3$ is monotone while $g(x):=x^2$ is not.

Noun

1. A single unvaried tone of speech or a sound

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

Adjective

1. Monotone
2. Whose speech is monotone.
3. Boring due to uniformity or lack of variety; monotonous.