Cosignitary
Co`sig´ni`ta`ry
| a. | 1. | Signing some important public document with another or with others; as, a treaty violated by one of the cosignitary powers. |
| n. | 1. | One who signs a treaty or public document along with others or another; as, the cosignitaries of the treaty of Berlin. |
Webster's Revised Unabridged Dictionary, published 1913 by G. & C. Merriam Co.