What does "supplement" mean?

Supplement: That which fills up, completes, or makes an addition to, something already organized, arranged, or set apart; specifically, a part added to, or issued as a continuation of, a book or paper, to make good its deficiencies or correct its errors.

Additional senses

  1. 2.(Trig.) The number of degrees which, if added to a specified arc, make it 180°; the quantity by which an arc or an angle falls short of 180 degrees, or an arc falls short of a semicircle. -- Appendix, Supplement. An appendix is that which is appended to something, but is not essential to its completeness; a supplement is that which supplements, or serves to complete or make perfect, that to which it is added.
  2. 3.To fill up or supply by addition; to add something to. Causes of one kind must be supplemented by bringing to bear upon them a causation of another kind. I. Taylor.

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