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Added 9 October 2026

rapidity

/ɹəˈpɪd.ɪ.ti/ noun

Latin root: rapiditas Wiktionary

noun Definition from Wiktionary (CC BY-SA). Pronunciation from Wiktionary, via Kaikki.org. More about rapidity at Wordnik → Where our words come from →

speed, swiftness; the condition of being rapid
A measure of velocity relative to the speed of light; defined as artanh(v), where artanh is the hyperbolic arctangent, and v = speed (with c = speed of light = 1).
A measure of the velocity of a particle in a beam relative to the beam's axis

Origin

From rapid + -ity, from French rapidité, from Latin rapiditas.

From Wiktionary, via Kaikki.org (CC BY-SA)

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