Douglas Harper's Etymology Dictionary
Wiktionary
a. (context economics English) at an equal rate adv. 1 simultaneously; likewise, equally. (from 16th c.) 2 (context economics legal English) At an equal rate.
WordNet
adv. used in legal language [syn: at an equal rate]
Wikipedia
Pari passu is a Latin phrase that literally means "with an equal step" or "on equal footing". It is sometimes translated as "ranking equally", "hand-in-hand", "with equal force", or "moving together", and by extension, "fairly", "without partiality".
Usage examples of "pari passu".
It is still in our power to direct the process of emancipation and deportation peaceably and in such slow degree as that the evil will wear off insensibly, and their place be pari passu filled up by free white laborers.
Those who advocated reformation of institutions, pari passu, with the progress of science, maintained that no definite limits could be assigned to that progress.
Really, Trent, these excuses grow more and more enfeebl'd, and tiresome pari passu What are you up to, honestly, when I leave you alone with this lovely Machine?