Definition: To acquire information by rumor or word-of-mouth. Also: heard it on the grapevine.
Origin: The phrase originated in the 1840-50s during the early days of the telegraph. The telegraph and Morse Code were developed by Samuel Morse and Alfred Vail in 1936 and beginning in 1844 telegraph lines were being strung throughout the eastern states (and eventually across the country). Early telegraph lines were crudely strung, so people likened them to sagging grapevines. Thus, “grapevine” was a shortened form of the “grapevine telegraph.” The phrase gained common usage during the Civil War (1861-65). The idea behind the phrase was not that rumors were actually sent by telegraph, but rather the enormous speed by which a rumor spreads.
The phrase was catapulted to fame by the hit song, “Heard it Through the Grapevine” sung by Marvin Gaye in 1968 (Gladys Knight and the Pips recorded an earlier version in 1967).
Today’s grapevine is the internet, fueled by tweets and texting, sending rumors and gossip around the world within seconds. Morse and Vail would truly be impressed.
For further reading: From the Horse’s Mouth: Oxford Dictionary of Idioms by John Ayto, Oxford University Press (2009); The Facts on File Encyclopedia of Word and Phrase Origins by Robert Hendrickson, Facts on File (2008); Random House Historical Dictionary of American Slang by J. E. Lighter, Random House (1994).