(adj): absolutely necessary; vitally necessary
(adj): necessary (for someone) as a duty or responsibility; morally binding
(adj): necessary for relief or supply
(adj): required by obligation or compulsion or convention
(adj): unavoidably determined by prior circumstances
(adj): vs. evitable) -- (incapable of being avoided or prevented
(n): anything indispensable
(n): a separate and self-contained entity
