Required, essential, whether logically inescapable or needed in order to achieve a desired result or avoid some penalty.
"Although I wished to think that all was false, it was yet necessary that I, who thus thought, must in some sense exist."
"It is absolutely necessary that you call and confirm your appointment."
"If it is absolutely necessary to use public computers, you should plan ahead and forward your e-mail to a temporary, disposable account."
Determined, involuntary: acting from compulsion rather than free will.
A necessary" business of urination and defecation: an outhouse or lavatory.
Not needed or necessary.
"The automatic child-frightener made clowns unnecessary."
Done in addition to requirements; unrequired.
"some people feel that holiday insurance is unnecessary"
more than is needed; excessive
"good construction is essential to avoid unnecessary waste"
"Flora never wasted cash on unnecessaries"
Such as must be; impossible to be otherwise; not to be avoided; inevitable.
Impossible to be otherwise, or to be dispensed with, without preventing the attainment of a desired result; indispensable; requisite; essential.
Acting from necessity or compulsion; involuntary; - opposed to free; as, whether man is a necessary or a free agent is a question much discussed.
A thing that is necessary or indispensable to some purpose; something that one can not do without; a requisite; an essential; - used chiefly in the plural; as, the necessaries of life.
A privy; a water-closet.
Such things, in respect to infants, lunatics, and married women, as are requisite for support suitable to station.
Not necessary; not required under the circumstances; unless; needless; as, unnecessary labor, care, or rigor.
"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"
unavoidably determined by prior circumstances;
"the necessary consequences of one's actions"