Monotonous means "all the same", and therefore it is used to mean boring, dull.
Some suggestions for antonyms:
interesting
exciting
varied
changing
changeable
unpredictable
heterogeneous
diverse
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whisper is the antonym of shout
consistent, invariable, monochrome, monophonic, monotonous, persistent, persisting, relentless, unchanging
Write "locomotion" and "monotonous" in your school-book, take it to the schoolroom, ...
Liking, ofcourse
rest