Adjectival nouns or quasi-adjectives (keiyodoshi); 必用 can imply has to be used rather than is just needed

necessary; needed; essential; indispensable

Common noun

necessity; need; requirement

to be needed; to be necessary; to be required; to be wanted; to need; to want

important; essential; significant; major; key; principal

demand; firm request; requisition; requirement; desire

unnecessary; not needed; not necessary

component; factor; item (e.g. in list)

Computing

element (e.g. in array); member (e.g. data structure)

to need; to call for; to require

in short; in a word; to sum up; to put it simply; to make a long story short; after all

Noun or participle which takes the aux. verb suru

appeal; call for something; request; claim; demand

axiom

unnecessary; unneeded