linkage (n.) Look up linkage at Dictionary.com
1874, from link (v.) + -age.
To understand the principle of Peaucellier's link-work, it is convenient to consider previously certain properties of a linkage, (to coin a new and useful word of general application), consisting of an arrangement of six links, obtained in the following manner ... (etc.). ["Recent Discoveries in Mechanical Conservation of Motion," in "Van Nostrand's Eclectic Engineering Magazine," vol. XI, July-December 1874]