Monotone

Monotone is a term used across several disciplines to describe a lack of variation in pitch, value, or order. It derives from the Latin mono- “one” and tonus “tone,” and in everyday usage it often refers to a voice or delivery that lacks inflection or expressiveness.

In general English usage, a monotone voice or speaking style is one that remains on a single pitch or shows little variation in pitch, tone, or intensity. The term can carry a negative connotation, suggesting dullness or monotony.

In mathematics and related fields, monotone describes a relation of order-preserving or order-reversing behavior. A function f is monotone increasing if x ≤ y implies f(x) ≤ f(y), and monotone decreasing if x ≤ y implies f(x) ≥ f(y). A sequence is monotone when it is entirely nondecreasing or nonincreasing. Monotone functions and sequences underpin convergence results such as the monotone convergence theorem; more generally, a map between ordered sets is monotone if it preserves the order. In order theory and analysis, monotone concepts extend to monotone classes, monotone operators, and related structures.

In computer science and logic, a monotone (or isotone) Boolean function preserves order under input changes: increasing inputs do not decrease the output. Monotone circuits use only operations that preserve monotonicity, such as AND and OR, without NOT.

In music, monotone can describe a melody or line that stays on a single pitch or lacks a clear melodic contour, though the term is used less formally than in speech.