Supplement, n.
Etymology: [F. supplément, L. supplementum, fr. supplere to fill up. See Supply, v. t.]
1. That which supplies a deficiency, or meets a want; a store; a supply. [Obs.] Chapman.
2. 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.
3. (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.
1 more senses
Syn. -- Appendix. -- 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.
1 other Webster entry under this spelling
Supplement, v. t. [imp. & p. p. Supplemented; p. pr. & vb. n. Supplementing.]
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.
Shades of meaning
Fernald has no entry of its own for supplement; he lists it under appendage.
Where he writes about it:
We add an appendix to a book, to contain names, dates, lists, etc., which would encumber the text; we add a supplement to supply omissions, as, for instance, to bring it up to date. — from appendage
An addition might be matter interwoven in the body of the work, an index, plates, editorial notes, etc., which might be valuable additions, but not within the meaning of appendix or supplement. — from appendage