<span>Monotonous is to dull, boring, tedious, droning or <span>repetitious </span></span>
Monotonous means the lack in variety.
<span> Musically speaking, it means an unvarying tone or pitch. But since your
analogy is started by an adjective, we have to pair it with an adjective too.
So you can pick one from any of these: dull, boring, tedious, droning or <span>repetitious </span></span>
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