TITLE: Monotonous function or monotonic function
QUESTION [6 upvotes]: I am from a non-English speaking country. Should we say monotonous function or monotonic function?

REPLY [2 votes]: monotonic  for sure is to be used.  Monotonic functions are those functions which are either increasing or decreasing. They are such that for each specific value of  x   there is a unique  y(value of function) which does not repeat for any other x.