monotony

noun

1. wearisome uniformity or lack of variety, as in occupation or scenery.
2. the continuance of an unvarying sound; monotone.
3. sameness of tone or pitch, as in speaking.

noun plural -nies

1. wearisome routine; dullness
2. lack of variety in pitch or cadence

n.1706, originally in transferred sense of “wearisome, tiresome,” from French monotonie (1670s), from Greek monotonia “sameness of tone, monotony,” from monotonos “monotonous, of one tone,” from monos “single, alone” (see mono-) + tonos “tone” (see tenet). Literal sense of “sameness of tone or pitch” in English is from 1724.