monotony

Uniformity or lack of variation in pitch, intonation, or inflection.

Tedious sameness or repetitiousness.

Uniformity of tone or sound; want of inflections of voice in speaking or reading; want of cadence or modulation; monotone.

Tiresome uniformity or lack of variation in any respect; sameness; want of variety.

In mathematics:

Continual increase, or continual decrease.

Unchanging character, neither increasing nor decreasing.

A frequent recurrence of the same tone or sound, producing a dull uniformity; absence of variety, as in speaking or singing.

Any irksome sameness, or want of variety.

Tedium as a result of repetition or a lack of variety.