sine qua non(n = noun.cognition) essential condition - a prerequisite; Array
is a kind of prerequisite, requirement

sine qua non, n. an indispensable condition or qualification.

Etymology:
L, = without which not

N  requirement, need, wants, necessities, necessaries, necessaries of life, stress, exigency, pinch, sine qua non, matter of necessity, case of need, case of life or death, needfulness, essentiality, necessity, indispensability, urgency, requisition, run upon, demand, call for, charge, claim, command, injunction, mandate, order, precept, desideratum, want, Adj, required, requisite, needful, necessary, imperative, essential, indispensable, prerequisite, called for, in demand, in request, urgent, exigent, pressing, instant, crying, absorbing, in want of, destitute of, ex necessitate rei, of necessity, there is no time to lose, it cannot be spared, it cannot be dispensed with, mendacem memorem esse oportet, necessitas non habet legem, nec tecum possum trivere nec sine te.

N  importance, consequence, moment, prominence, consideration, mark, materialness, import, significance, concern, emphasis, interest, greatness, superiority, notability, weight, value, usefulness, gravity, seriousness, solemnity, no joke, no laughing matter, pressure, urgency, stress, matter of life and death, memorabilia, notabilia, great doings, red-letter day, great thing, great point, main chance, the be all and the end all, cardinal point, substance, gist, sum and substance, gravamen, head and front, important part, principal part, prominent part, essential part, half the battle, sine qua non, breath of one's nostrils, cream, salt, core, kernel, heart, nucleus, keynote, keystone, corner stone, trump card, salient points, top sawyer, first fiddle, prima donna, chief, triton among the minnows, 'it', important, of importance, momentous, material, to the point, not to be overlooked, not to be despised, not to be sneezed at, egregious, weighty, of note, notable, prominent, salient, signal, memorable, remarkable, unforgettable, worthy of remark, worthy of notice, never to be forgotten, stirring, eventful, grave, serious, earnest, noble, grand, solemn, impressive, commanding, imposing, urgent, pressing, critical, instant, paramount, essential, vital, all-absorbing, radical, cardinal, chief, main, prime, primary, principal, leading, capital, foremost, overruling, of vital importance in the front rank, first-rate, superior, considerable, marked, rare, significant, telling, trenchant, emphatic, pregnant, tanti, materially, in the main, above all, kat' exochin, par excellence, to crown all, to beat all, expende Hannibalem!.

N  conditions, terms, articles, articles of agreement, memorandum, clauses, provisions, proviso, covenant, stipulation, obligation, ultimatum, sine qua non, casus foederris, conditional, provisional, guarded, fenced, hedged in, conditionally, provisionally, pro re nata, on condition, with a string to it.

N  qualification, limitation, modification, coloring, allowance, grains of allowance, consideration, extenuating circumstances, mitigation, condition, proviso, prerequisite, contingency, stipulation, provision, specification, sine qua non, catch, string, strings attached, exemption, exception, escape clause, salvo, saving clause, discount, restriction, fine print, qualifying, qualified, conditioned, restricted, hedged, conditional, exceptional, hypothetical, contingent, provided, provided that, provided always, if, unless, but, yet, according as, conditionally, admitting, supposing, on the supposition of, with the understanding, even, although, though, for all that, after all, at all events, approximately, in a limited degree (smallness), somewhat, sort of, something like that, to a certain extent, to a degree, in a sense, so to speak, with grains of allowance, cum grano salis, with a grain of salt, exceptis excipiendis, wind and weather permitting, if possible, subject to, conditioned upon, with this proviso, if the good lord is willing and the creeks don't r, catch-, Degrees of Evidence.

arc sine, coversed sine, inverse sine, latino sine flexione, non, non assumpsit, non compos, non compos mentis, non est factum, non est inventus, non liquet, non obstante, non pros, non pros., non prosequitur, non sequitur, non vult, persona non grata, qua, sine, sine curve, sine die, sine wave