Plural of grapevine; woody vines that produce grapes, or informally, a system of gossip and informal information sharing (as in 'I heard it through the grapevine').
From 'grape' plus 'vine,' straightforward compound. The slang meaning (informal communication network) emerged in American English, likely from the visual resemblance of spreading grapevines to spreading rumors and information.
The phrase 'I heard it through the grapevine' is brilliantly metaphorical—grapevines spread messily and sprawl everywhere, which mirrors how gossip spreads unpredictably and reaches unexpected people. Songs used this metaphor because it captures the chaotic, organic nature of rumor spreading.
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