n. A jet contrail that has been laced with chemical or biological agents. Also: chem-trail, chem trail.

Example Citations:
Wonder how the Bush administration arranged for the destruction of the World Trade Center? Curious why the government planes are releasing toxic chemtrails into our atmosphere? Step right up, because for a record 26 days, KPFK-FM (90.7) not only provided answers but offered to hook you up with that sweet DVD set, unveiling the fuller, darker truth.
—James Rainey, "Schism at KPFK leaves factions warring over programming, fundraising and leadership," Los Angeles Times, March 27, 2010

Ah, the old "chemtrail conspiracy" theory. The idea that the white lines of condensed water vapor that you see following planes, contrails, are really a toxic substance intentionally being sprayed on people by the government has been around at least since 1996.
—"Q&A: Government is not spraying chemicals," St. Petersburg Times, June 1, 2010

Earliest Citation:
So Levinson - and plenty of cohorts on the Internet, not to mention one well-known AM radio talk show host — are spreading the word about "chemtrails," as they call them. Levinson et al say the trails contain bacteriological pathogens and an assortment of toxic chemicals. The government is "spraying" our fair skies for dark, dark reasons.
—John Boyle, "'Chemtrails' heat up Asheville skies," The Asheville Citizen-Times, March 22, 1999

For more than you probably want to know about the chemtrail "conspiracy," or if you simply enjoy thorough refutations (or, I guess, refudiations) of this kind of thing, see the chemtrails entry in The Skeptic's Dictionary.

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