necessity (
http://definr.com/necessity)
n 1: the condition of being essential or indispensable
2: anything indispensable; "food and shelter are necessities of
life"; "the essentials of the good life"; "allow farmers
to buy their requirements under favorable conditions"; "a
place where the requisites of water fuel and fodder can be
obtained" [syn:
essential,
requirement,
requisite,
necessary]
[ant:
inessential]