ETYMOLOGY: What Are Chemtrails?
Etymology: def: "the study of the origin of words and the way in which their meanings have changed throughout history."
Here is solid fact-based answer you can give when somebody asks you to explain "chemtrails"
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The origin of the word chemtrails can be traced to the year 1990 when the DoD printed a US Air Force Academy chemistry manual titled CHEMTRAILS - a project funded by the American taxpayer. [ Chemtrails Manual (PDF) ]
The word "chemtrails" has no meaning ascribed to it in the text of the chemistry manual, however the "chemtrails" term soon gained popularity outside of the Air Force and was adopted by civilian sky observers to describe unusual aircraft emissions and/or contrail formations.
In fact, a NASA scientist (Doug Rowland, PhD) actually used the word "chemtrails" to describe plumes of emission trails resulting from rocket experiments launched into the atmosphere.
https://archive.org/details/ChemtrailsManualChemistry131ManualUSAFAcademyFall1990_201810/page/n199