Reportedly, use of the word "plasma" in reference to ionized gas was
coined by a gentleman by the name of Irving Langmuir, who was doing
electrical research during the 1920s. The following is quoted from
this webpage: http://www.plasmacoalition.org/what.htm...
"During the 1920's Irving Langmuir was studying various types of
mercury-vapor discharges, and he noticed similarities in their
structure - near the boundaries as well as in the main body of the
discharge. While the region immediately adjacent to a wall or
electrode was already called a "sheath," there was no name for the
quasi-neutral stuff filling most of the discharge space. He decided to
call it "plasma."
While his relating the term to blood plasma has been acknowledged by
colleagues who worked with him at the General Electric Research
Laboratory, , , the basis for that connection is unclear. One
version  of the story has it that the similarity was in carrying
particles, while another account  speculated that it was in the
Greek origin of the term, meaning "to mold," since the glowing
discharge usually molded itself to the shape of its container. In any
case, it appears that the first published use of the term was in
Langmuir's "Oscillations in Ionized Gases," published in 1928 in the
Proceedings of the National Academy of Sciences .
Thus the term "plasma" was first used to describe partially (if not
weakly) ionized gases. The term plasma apparently did not find
immediate widespread use in the scientific community. It did
eventually catch on, however, but in some cases the term was
inappropriately limited to highly ionized gases.
 L. Tonks, "The birth of 'plasma'" Amer. J. Phys., vol. 35, pp. 857-858, 1967.
 Letter from H. M. Mott-Smith to A. M. Bueche, Apr. 20, 1967 (on
file at Communications Operation, General Electric R&D Center,
 S. C. Brown, "A short history of gaseous electronics," in Gaseous
Electronics, vol. 1, M. N. Hirsh and H. J. Oskam, Eds. New York:
Academic, 1978, pp. 1-18.
 I. Langmuir, "Oscillations in ionized gases," Proc. Nat. Acad.
Sci. U.S., vol. 14, p. 628, 1928; also available in The Collected
Works of Irving Langmuir, vol. 5, C. G. Suits, Ed. New York: Pergamon,
1961, pp. 111-120."