(1):

(n.) The act of linking; the state of being linked; also, a system of links.

(2):

(n.) 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.

(3):

(n.) Manner of linking or of being linked; - said of the union of atoms or radicals in the molecule.