Collins English-English Dictionary

necessary ['nεsɪsərɪ]

1. 1. adj needed to achieve a certain desired effect or result; required

2. 2. adj resulting from necessity; inevitable

   the necessary consequences of your action

3. 3. adj [logic] (of a statement, formula, etc) true under all interpretations or in all possible circumstances

4. 4. adj (of a proposition) determined to be true by its meaning, so that its denial would be self-contradictory

5. 5. adj (of a property) essential, so that without it its subject would not be the entity it is

6. 6. adj (of an inference) always yielding a true conclusion when its premises are true; valid

7. 7. adj (of a condition) entailed by the truth of some statement or the obtaining of some state of affairs

8. 8. adj Compare sufficient

9. 9. adj [philosophy] (in a nonlogical sense) expressing a law of nature, so that if it is in this sense necessary that all As are B, even although it is not contradictory to conceive of an A which is not B, we are licensed to infer that if something were an A it would have to be B

10. 10. adj [rare] compelled, as by necessity or law; not free

11. 11. n See also necessaries

12. 12. n [Etymology] C14: from Latin necessarius indispensable, from necesse unavoidable