ἀρχή:

Greek, noun, beginning, origin, foundation, source

 

ὕλη:

Greek, noun forest, woodland, stuff, material, matter

 

Ent: * see EndNote<A>

Greek word meaning that which exists.  Spengler is referencing a lost work by Gorgias, a Greek pre-Socratic, first generation Sophist, who wrote On Nature or the Non-Existent, an ironic refutation of Parmenides' thesis on Being.  In this he refers to the Ent (that which “is”) and the Nonent (“that which “is not”)

 

plenum:

a space or all space every part of which is full of matter

 

das Raumerfullende:

German, space filling

 

wave-motion of light: * see EndNote<B>

a theory which emerged in the 17th century but was only proven in the mid-19th century by Foucault, Faraday and Maxwell.  It was once considered incompatible to the particle theory

 

luminiferous aether:

a phrase literally meaning the production of light by the rarefied element once believed to fill the upper regions of space or heaven.  It was proposed by Christiaan Huygens (1629–1695) who worked out a mathematical wave theory of light in 1678 (published 1690 in his Treatise on light).  He proposed light was emitted in all directions as a series of waves in a medium called the Luminiferous ether.  As waves are not affected by gravity, it was assumed that they slowed down upon entering a denser medium.

 

ascription:

verb, to refer to a supposed cause, source or author; to say or think that something is caused by, comes from, or is associated with a particular person or thing

 

Nonent:

something that does not exist

and see Ent above