monotony (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.