Definition - Language that is used to deliberately conceal the speaker's true intentions.

Example -
In 1977 National Airlines called the crash of one of its airplanes an "involuntary conversion of a 727." They were purposely using jargonny legal doublespeak to mislead their stockholders.

Etymology -
The word was probably coined by blending the terms doublethink and newspeak. According to the Oxford Companion to the English Language, it was first used in this sense in 1971 by the National Council of Teachers of English.

Oxford English Dictionary -
It first citation is from 1957, but its first citation in this sense is from 1970:
"Double-speak in America."
(M. Pei Words in Sheep's Clothing i. 1 (heading) )

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