rhythm

English rhythm was coined in 1557 from Latin rhythmus, itself borrowed from Ancient Greek ῥυθμός (rhuthmós), meaning any measured flow or movement. That Greek word comes from ῥέω (rhéō), "to flow, run, stream, gush," tracing back through Proto-Hellenic to a Proto-Indo-European root meaning "to flow."

The sense narrowed over time from a general "measured flow or movement" in Greek to the more specific musical and poetic "beat" we mean by rhythm in English today.

Its root sense of flowing connects it to the Greek verb rhéō, "to flow," the very idea that gave rhythm its name.