Such as must be; impossible to be otherwise; not to be avoided; inevitable.
- Absolutely essential. See Synonyms at indispensable.
- Needed to achieve a certain result or effect; requisite: the necessary tools.
- Unavoidably determined by prior conditions or circumstances; inevitable: the necessary results of overindulgence.
- Logically inevitable.
- Required by obligation, compulsion, or convention: made the necessary apologies.
- Something indispensable.