(n.) unintelligible language; birdsong
He was al coltissh, ful of ragerye,
And ful of jargon as a flekked pye.
The slakke skyn aboute his nekke shaketh,
Whil that he sang, so chaunteth he and craketh.
Geoffrey Chaucer, The Canterbury Tales (c. 1386)
These lines are taken from Chaucer’s Merchant’s Tale, written in the late fourteenth century. Here, the ageing and vain lothario January has just joined his twenty-something new bride May in bed on their wedding night, and serenaded her with a song that “shakes the slack skin around his neck.” What a lucky woman she is.
In Chaucer’s words, January is “full of jargon like a flecked pie,”—that is, a magpie. If that seems like a failed metaphor, then here’s the missing piece of the puzzle: jargon was originally a word for birdsong.
The word jargon was borrowed into English from French in the early fourteenth century. It is believed to have begun life as another word for birdsong, or more generally the constant wittering or chattering sounds of birds—in which case it was probably originally onomatopoeic, and somehow intended to imitate a chirping or chirruping sound. (If that’s the case, then jargon might have an unlikely etymological cousin in cajole, which is thought to derive from an Old French word meaning ‘to chatter like a jay’ and probably originally referred to the act of enticing or ‘cajoling’ a bird into a cage or trap.)
But because birdsong is all but unintelligible to us, it didn’t take long for jargon to come to be used of any equally unintelligible chatter or talk. This meaning was already present in French by the time English adopted the word jargon in the mid 1300s, and both meanings—birdsong and nonsense talk—arrived in the language around the same time.
Here in Chaucer’s Merchant’s Tale, both meanings are being played on simultaneously: January is serenading his wife (albeit not particularly well), but he could just as easily be chattering away inanely and unintelligibly “like a flecked pie.”
The use of jargon as another word for birdsong all but disappeared in the fifteenth century, while its use as another word for prattle or nonsense-speak thrived. By the early sixteenth century, it was being applied to encrypted, symbol-based writing; by the early seventeenth century, it was being used of muddled and hybridized mixtures of languages, and conversations between multilingual speakers that slip from one language to another; and by the mid seventeenth century, the modern sense—of language that is (either intentionally or unintentionally) full of technical terminology and esoteric vocabulary—finally emerged.
A derivative verb, jargonize, followed on in the early nineteenth century, while someone who uses jargon in their everyday speech has been called a jargonist since the late 1700s.