Synonyms/Hypernyms (Ordered by Estimated Frequency) of noun necessary

1 sense of necessary

Sense 1
necessity, essential, requirement, requisite, necessary -- (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")
       => thing -- (a separate and self-contained entity)

Antonyms of adj necessary

2 senses of necessary

Sense 1
necessary (vs. unnecessary) -- (absolutely essential)

unnecessary (vs. necessary), unneeded -- (not necessary)
        => excess, extra, redundant, spare, supererogatory, superfluous, supernumerary, surplus -- (more than is needed, desired, or required; "trying to lose excess weight"; "found some extra change lying on the dresser"; "yet another book on heraldry might be thought redundant"; "skills made redundant by technological advance"; "sleeping in the spare room"; "supernumerary ornamentation"; "it was supererogatory of her to gloat"; "delete superfluous (or unnecessary) words"; "extra ribs as well as other supernumerary internal parts"; "surplus cheese distributed to the needy")
        => gratuitous, needless, uncalled-for -- (unnecessary and unwarranted; "a strikers' tent camp...was burned with needless loss of life")
        => inessential -- (not absolutely necessary)
        => spare -- (kept in reserve especially for emergency use; "a reserve supply of food"; "a spare tire"; "spare parts")

Sense 2
necessary -- (unavoidably determined by prior circumstances; "the necessary consequences of one's actions")

INDIRECT (VIA inevitable) -> evitable, avoidable, avertible, avertable -- (capable of being avoided or warded off)

Similarity of adj necessary

2 senses of necessary

Sense 1
necessary (vs. unnecessary) -- (absolutely essential)
       => essential, indispensable -- (absolutely necessary; vitally necessary; "essential tools and materials"; "funds essential to the completion of the project"; "an indispensable worker")
       => incumbent -- (necessary (for someone) as a duty or responsibility; morally binding; "it is incumbent on them to pay their own debts")
       => needed, needful, required, requisite -- (necessary for relief or supply; "provided them with all things needful")
       => obligatory -- (required by obligation or compulsion or convention; "he made all the obligatory apologies")
          Also See-> essential#2; indispensable#1; obligatory#1

Sense 2
necessary -- (unavoidably determined by prior circumstances; "the necessary consequences of one's actions")
       => inevitable (vs. evitable) -- (incapable of being avoided or prevented; "the inevitable result")