requisite

Etymology

From Latin requīsītus, perfect passive participle of requīrō (“I require, seek, ask for”), from which English require.

adj

1. Essential, indispensable, required.
   Please submit the requisite papers before the end of the financial year.
   On the other hand, there will be widespread agreement with Sir Brian's belief that, when a British main line has been completely dieselised and the schedules have been recast to suit the new traction, much higher daily mileages than 350 are not only possible but requisite, at least in the early stages of dieselisation. 1961 July, “Editorial: Sir Brian begs the questions”, in Trains Illustrated, page 386

noun

1. An indispensable item; a requirement.
   But this something, what is it, unless the happiness of others, or some of the requisites of happiness? 1861, John Stuart Mill, Utilitarianism
   The main requisite is to brew a tasty, palateful and wholesome beer […] 1904, Letters on Brewing, volume 3, page 127