It looks like "extropy" as a term has multiple origins.
Ed Close stated in a posting to the quantum-d mailing list:
"I. Regarding Joel Henkel's definition of "extropy":
In general, I like Joel's ideas, but the term "extropy" is not new. As far as I am aware, use of the term "extropy" originated with work I did beginning in 1986 and published in 1990. However, extropy is such a natural concept that someone else may have coined the term prior to 1990.
Our definitions are similar. The word "extropy" is defined on Page 36 of my book (see following quotes) and was used to describe the mirror image of entropy.
'...the organizing force existing prior to relative
motion... Ex = before or beyond, tropy = turning or relative motion.'"
His posting can be found at:
Evidently, Close "coined" and defined the term in his book