1550s, "net-like arrangement of threads, wires, etc., anything formed in the manner of or presenting the appearance of a net or netting," from net (n.) + work (n.). Extended sense of "any complex, interlocking system" is from 1839 (originally in reference to transport by rivers, canals, and railways). Meaning "broadcasting system of multiple transmitters" is from 1914; sense of "interconnected group of people" is by 1934 in psychology jargon.
1887, "to cover with a network," from network (n.). From 1940 as "to broadcast over a (radio) network;" 1972 in reference to computers; by 1982 in reference to persons, "to interact with others to exchange information and develop contacts." Related: Networked; networking.