Monotony (noun)
Tedium as a result of repetition or a lack of variety.
Monotony (noun)
The property of a monotonic function.
Monotony (noun)
The quality of having an unvarying tone or pitch.
Monotonous (adjective)
Having an unvarying tone or pitch.
Monotonous (adjective)
Tedious, repetitious or lacking in variety.
Wiktionary
Monotony (noun)
lack of variety and interest; tedious repetition and routine
“you can become resigned to the monotony of captivity”
Monotony (noun)
sameness of pitch or tone in a sound or utterance
“depression flattens the voice almost to monotony”
Oxford Dictionary