Supplement

That which supplies a deficiency, or meets a want; a store; a supply.

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.

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.

To fill up or supply by addition; to add something to.