Mid 16th century; earliest use found in Thomas Elyot (c1490–1546), humanist and diplomat. From classical Latin rhythmus (also rythmus) sequence of sounds forming a pattern, (specifically) measured flow of words or phrases in prose, in post-classical Latin also harmony, harmonious part, verse (especially accentual, syllabic as opposed to quantitative verse), pattern of stressed and unstressed syllables, sequence of sounds forming a pattern, a poem, verse, or song, especially a light one from ancient Greek ῥυθμός measured motion, time, measured flow of words or phrases in prose, measure, proportion, symmetry, arrangement, order from an ablaut variant of the base of ῥεῖν to flow + -θμος, extended form of -μος, suffix forming nouns. Compare later rhythm.