What does "necessary" mean?

Necessary: Impossible to be otherwise, or to be dispensed with, without preventing the attainment of a desired result; indispensable; requiste; essential. "'T is necessary he should die." Shak. A certain kind of temper is necessary to the pleasure and quiet of our minds. Tillotson.

Additional senses

  1. 2.Acting from necessity or compulsion; involuntary; -- opposed to free; as, whether man is a necessary or a free agent is a question much discussed.
  2. 3.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.
  3. 4.A privy; a water-closet.
  4. 5.pl. (Law) Such things, in respect to infants, lunatics, and married women, as are requisite for support suitable to station.

Sources