rapidity n. + Add to list US //ɹəˈpɪdəti// UK //ɹæpˈɪdɪti// ra·pid·i·ty SynonymsEtymology Synonyms celerityquicknessrapidnessspeedinessOriginLATrapiditas→FRArapidité→ENrapidity From rapid + -ity, from French rapidité, from Latin rapiditas.