Req·ui·site, a. Required by the nature of things, or by circumstances; so needful that it can not be dispensed with; necessary; indispensable.
All truth requisite for men to know. --Milton.
Syn: -- Necessary; needful; indispensable; essential.
-- Req*ui*site*ly, adv. -- Req*ui*site*ness, n.
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requisiteness
n : the state of being absolutely required