n. 1. The act of linking; the state of being linked; also, a system of links. [ 1913 Webster ]
2. (Chem.) Manner of linking or of being linked; -- said of the union of atoms or radicals in the molecule. [ 1913 Webster ]
3. (Geom.) A system of straight lines or bars, fastened together by joints, and having certain of their points fixed in a plane. It is used to describe straight lines and curves in the plane. [ 1913 Webster ]
4. Any object, factor, or relationship that creates a bond or association between two other objects. [ PJC ]
5. Specifically: (Genetics) The proximity of two or more genes on the genome of an organism that causes those genes to be inherited, transferred, or moved together with a frequency greater than for genes not associated. The linkage is a continuous variable, and is inversely related to the distance between genes on the genome. [ PJC ]