Astral is a word that derives from the Latin astrum and from the Greek astron, meaning "star", and refers to a plane consisting of a subtler kind of matter, held to be next above the physical world in refinement.
H. P. Blavatsky wrote:
The designation astral is ancient, and was used by some of the Neoplatonists. Porphyry describes the celestial body which is always joined with the soul as “immortal, luminous, and star-like.” The root of this word may be found, perhaps, in the Scythic aist-aer — which means star, or the Assyrian Istar, which, according to Burnouf has the same sense.
This inner world is called Astral by some people, and it is as good a word as any other, though it merely means starry; but the stars, as Locke pointed out, are luminous bodies which give light of themselves. This quality is characteristic of the life which lies within matter; for those who see it, need no lamp to see it by. The word star, moreover, is derived from the Anglo-Saxon "stir-an," to steer, to stir, to move, and undeniably it is the inner life which is master of the outer, just as a man's brain guides the movements of his lips. So that although Astral is no very excellent word in itself, I am content to use it for my present purpose.
Although the word "astral" was frequently used by Blavatsky to refer to non-physical principles or bodies, on some occasions she used it in a more general way to refer to things of a composition similar to the jellyfish:
The word "astral" does not necessarily mean as thin as smoke, in occult phraseology, but rather "starry," shining or pellucid, in various and numerous degrees, from a quite filmy to a viscid state.
- Helena Petrovna Blavatsky, Isis Unveiled vol. I, (Wheaton, IL: Theosophical Publishing House, 1972), xxv.
- Helena Petrovna Blavatsky, The Secret Doctrine vol. I, (Wheaton, IL: Theosophical Publishing House, 1993), 16.
- Helena Petrovna Blavatsky, The Secret Doctrine vol. II, (Wheaton, IL: Theosophical Publishing House, 1993), 251.