1706, originally in transf. sense of "wearisome, tiresome," from Fr.
monotonie, from Gk.
monotonia, from
monotonos "monotonous, of one tone," from
monos "single, alone" +
tonos "tone" (see
tenet). Literal sense of "sameness of tone or pitch" is from 1724.
Monotone "an unvarying tone in music or speaking" is first attested 1644;
monotonous is first recorded 1778; transf. sense of "lacking in variety, uninteresting" is from 1791.