From the A Word A Day mailing list
ylem (I-lum) noun
A form of matter hypothesized by proponents of the big bang theory
to have existed before the formation of the chemical elements.
(Middle English, universal matter, from Old French ilem, from Medieval
Latin hylem, accusative of hyle, matter, from Greek hule.)
"Alpher and Gamow focused on the point when the universe had cooled to a
state consisting of radiation and matter, ylem, Greek for the primordial
stuff of life."
Joseph D'Agnese, "The last Big Bang man left standing", Discover, Jul. 1999.