Contrary to rumors of “conspiracy theory”, the Department of Defense first published “Chemtrails” in 1990 as the title to a chemistry course for new pilots attending the esteemed US Air Force Academy. The term “Chemtrails”, and its implied meaning was eventually adopted by civilian observers to describe unusual jet contrail emissions.
Subsequent editions of “Chemtrails” have been published. Several 1998 editions were found for sale at BOOKFINDERS4U (ISBN: 0201306840 – ISBN-13: 9780201306842) Publisher: Addison Wesley Publishing Company.  Price = $142.00 [Also available on Amazon]
In 2001, US Rep., Dennis Kucinich introduced HR 2977 “Space Preservation Act of 2001″. The text of the Bill defines Chemtrails as an exotic weapon. 
To their credit, the Oxford dictionary provides an accurate description of chemtrails even if they failed to list the US DoD as the original publisher.
Oxford Dictionary Defines “Chemtrail”
chemtrail – Syllabification: (chem·trail) – Pronunciation: /ˈkemˌtrāl/Definition of chemtrail noun
“a visible trail left in the sky by an aircraft and believed by some to consist of chemical or biological agents released as part of a covert operation.”
Origin: 1990s blend of chemical and trail, on the pattern of contrail. 
In etymological terms, the origin of a word is very important. Regardless the intended definition, history clearly shows the term “Chemtrails” originated at the US Department of Defense as the title for a Chemistry manual used at the Air Force Academy cadet training program in the early 1990′s. Two editions of the “Chemtrails” manual are known to exist – A 200 page version for the 1990 Fall class and a 232 page version for the 1991 class. The course title “chemtrails” was so popular as to be adopted by the DoD for at least two academic years (1990-1991).
About the Chemtrails Manual Cover
– The Air Force Academy Chemtrails manual cover shows a flame from a Bunsen burner that appears to be producing two “trails”.
– The title of the manual “Chemtrails” is printed between the two “trails”.
– Considering the intentional graphic depicting “trails” it’s possible the Bunsen burner represents a jet engine producing “chemically” induced, persistent contrails.
– A Bunsen burner is a common piece of laboratory equipment that produces a single open gas flame which is used for heating, sterilization, and combustion.
– A test tube filled with a liquid is emptying contents into a flask.
– The remaining graphic appears to be a chemical representation for “methane” (CH4). Since Natural gas contains mostly “methane” it’s possible this symbol alludes to the fuel providing the flame to the Bunsen burner. [4 – Natural Gas]
Method: An inter-library loan from the Alachua County main library yielded a microfilm copy of the 1990 Chemistry 131 Manual used in training by the US Air force Academy. The lending institution was the William T. Young Library at the University of Kentucky as shown in the label below.
The microfilm was in acceptable condition, however the 1990 Chemtrails manual was scanned in 1992 under less than optimum conditions from a well-used original.
The Alachua County Library equipment was used to scan each of the 200 pages to digital *.TIF files. Photoshop was used to optimize each image to the smallest file size that would permit adequate resolution for on-line viewing. Each image was imported to a Microsoft Word page where the complete manual was saved to a 30 MB PDF file. (Portable Document File).
NOTE: A second edition of Chemtrails (232 pages) was published for a subsequent Fall class of Air Force cadets. (Circa 1992)
Disclaimer: The purpose of this post is to establish the term “chemtrails” was invented by the DoD and USAFA. However compelling, we resist claiming that the title and/or content is directly linked to the covert aerosol geoengineering and “chemtrails” operation that has been infecting planet earth for the past quarter century. The course content, however suggests an intent to manipulate atmospheric chemistry and could be construed as a course requirement for pilots who could be engaged in deploying chemicals into the atmosphere.