This is the 13273rd most frequent Russian word.
монотонных
Monotonous.
Here, 'монотонных' describes the repeated or unvaried nature of the duties.
Она устала от монотонных обязанностей.
She was tired of monotonous duties.
In this instance, 'монотонных' characterizes activities that lack variation or excitement.
Учитель говорил о вреде монотонных занятий.
The teacher spoke about the harm of monotonous activities.
In this case, 'монотонных' pertains to sounds that are uniform in tone or rhythm, lacking diversity.