I . a.
1.
Inevitable, unavoidable, that must be.
2.
Requisite, essential, indispensable, needful, that cannot be spared.
3.
Involuntary.
II . n.
1.
Requisite, requirement, necessity, essential, indispensable thing, sine qua non .
2.
Privy, jakes, water-closet, back-house.