Definition of ylem in English:

ylem

Pronunciation /ˈīləm/ /ˈaɪləm/

noun

Astronomy
  • (in the Big Bang theory) the primordial matter of the universe, originally conceived as composed of neutrons at high temperature and density.

    • ‘We had to use primordial ylem.’

Origin

1940s from late Latin hylem (accusative) ‘matter’.