Noun

1. Something added, especially to make up for a deficiency.
2. An extension to a document or publication that adds information, corrects errors or brings up to date.
3. An additional section of a newspaper devoted to a specific subject.
4. An angle that, when added to a given angle, makes 180°; a supplementary angle.
5. : A vitamin, herbal extract, or chemical compound included with a diet to enhance muscular development.

Verb

1. To provide or make a supplement to something.