Monotone(n.) A single unvaried tone or sound.
Monotone(n.) The utterance of successive syllables, words, or sentences, on one unvaried key or line of pitch.
Monotonic(a.) Alt. of Monotonical
Monotonical(a.) Of, pertaining to, or uttered in, a monotone; monotonous.
Monotonous(a.) Uttered in one unvarying tone; continued with dull uniformity; characterized by monotony; without change or variety; wearisome.

Words within monotonicity