ylem

ylem puhekieltä In the Big Bang theory, the hot and dense plasma which made up the cosmos at the time of recombination in an early stage of its expansion and cooling, when the first atoms formed and photons decoupled. The ylem is regarded as the source of the cosmic microwave background. (defdate)
(quote-journal)|location=College Park, Md.|publisher=(w)|date=1 December 1948|vol=74|issue=11|page=1581, column 1|doi=10.1103/PhysRev.74.1577|oclc=896770069|passage=Very shortly after the beginning of the universal expansion, the ylem was a gas of neutrons only. Footnote: According to Webster's New International Dictionary, 2nd Ed., the word ‘ylem’ is an obsolete noun meaning ‘The primordial substance from which the elements were formed.’ It seems highly desirable that a word of so appropriate a meaning be resurrected.
1952, (w), The Creation of the Universe, New York, N.Y.: (w), (w) http://www.worldcat.org/oclc/999160 999160; republished as New York, N.Y.: Viking Press, 1961, 2nd edition, (w) http://www.worldcat.org/oclc/642243549 642243549, page 53:

Let us now consider the state of matter during the first minutes of the expansion process, when the temperature of the universe was many billions of degrees high. (..) The state of matter must be visualized as a hot gas formed entirely by nuclear particles; that is, protons, neutrons, and electrons. (..) We will call this primordial mixture of nuclear particles "Ylem," footnote: Pronounced: ī′lěm reviving an obsolete noun which, according to Webster's Dictionary, means "the first substance from which the elements were supposed to be formed." Next we can ask what happened to the Ylem when its density and temperature began to drop as the result of the rapid expansion taking place in the young universe.