monotony

nouns

the quality of wearisome constancy, routine, and lack of variety
"he had never grown accustomed to the monotony of his work"; "he was sick of the humdrum of his fellow prisoners"; "he hated the sameness of the food the college served"
humdrum, monotony, sameness
constancy of tone or pitch or inflection
monotony
is a type of (narrower)
the quality of being enduring and free from change or variation
"early mariners relied on the constancy of the trade winds"
constancy, stability