1560s, "any short piece of writing" (especially poetry), from line (n.) in the sense "row of verse," attested since late Old English (answering to Latin versus, Greek stikhos). Hence "a few words in writing, a short letter" (1640s); meaning "words of an actor's part" is from 1882. From 1670s as "outlines, plans" (of a building, ship, etc.); hence, figuratively, "plan, model" of anything (1757). Lines of communication originally were transverse trenches in siegeworks, from line (n.) in a military sense "trench, rampart," a collective singular from 1690s given a new currency in World War I.
updated on July 22, 2016