noun which may take the genitive case particle 'no', noun
necessary; essential; indispensable
Used primarily as a noun modifier (〜の) or in compounds; often refers to things that are essential for a purpose. Not typically used as a standalone predicate like 必要.
Water is essential for living.
This tool is an essential item for mountain climbing.
不要 means 'unnecessary, not needed', the direct opposite of 必需's sense of being indispensable.
必需 almost always appears bound in 必需品 ('daily necessity') and cannot stand alone as an adjective, unlike 必携 which is freely used with の or as a suffix.
necessity; essential item; must-have
Compound of 必 (certainly, inevitably) and 需 (demand, need). The exact historical derivation is uncertain, but the spelling is conventionally associated with the meaning of essential need.