monotony

noun3

1. •
   Tedium as a result of repetition or a lack of variety.

   • It matters little to trace the rapidity of the land journey, or the monotony of the sea voyage—alike unmarked by adventure. Robert Evelyn landed at Southampton,... — 1834
2. •
   The quality of having an unvarying tone or pitch.
3. •
   The property of a monotonic function.