An item that one must own, or a feature that is essential to a service, etc.
Essential to own.
Something necessary; a requisite; something indispensable.
Something which makes an act or an event unavoidable; an irresistible force; overruling power.
Greater utilitarian good; used in justification of a criminal act.
Indispensable requirements (of life).
The negation of freedom in voluntary action; the subjection of all phenomena, whether material or spiritual, to inevitable causation; necessitarianism.
The condition of being needy; desperate need; lack.
The quality or state of being necessary, unavoidable, or absolutely requisite.