(n.) A previous or antecedent condition; a preliminary condition.

arrangement bare necessities basic training boundary condition briefing call for called for catch clause clearing the decks condition demand demand for demanded desideration desideratum donnee equipment escalator clause escape clause escape hatch essential essentials familiarization fine print fixing foundation given grounds groundwork imperative indicated indispensable irreducible irreductible irreplaceable joker kicker limiting condition makeready making ready manufacture mobilization must must item necessaries necessary necessities necessitous necessity need need for needed needful obligation obligatory occasion parameter planning prearrangement precondition preliminaries preliminary preliminary act preliminary step prep preparation preparative preparatory preparatory study preparing prepping prerequirement pretreatment processing propaedeutic provident provision provisional provisions proviso qualification readying required requirement requisite requisition saving clause sine qua non small print spadework specification stipulation string terms the necessary the needful training treatment trial tryout ultimatum unforgoable vital want wanted warm-up whereas