pa·ri pas·su \ˌparēˈpa(ˌ)sü, -rə̇ˈp-; ˌpärēˈpä(ˌ)sü\adverb (or adjective) Etymology: Latin, with equal step : at an equal rate or pace : with identical and simultaneous progression < the rate of development decreased pari passu with the density — Ecology > < the two made a pari passu advance >