TITLE: Is "monotonous" ever used as a synonym for "monotonic" in math?
QUESTION [8 upvotes]: I saw a few questions and answers recently that wrote "monotonous" instead of "monotonic."  Then I Googled and see a ton of usages of "monotonous" in M.SE instead of monotonic.
It occurred to me this might be a locale issue. Are there any locales that actually use "monotonous" for "monotonic" in English-language mathematics, or is this always wrong?

REPLY [11 votes]: It is always wrong. It is a clear error, which a native English-speaking mathematician would never commit.