Consciousness is the fundamental energy, and the psychic energy is its highest quality. (LHR I, p 499)
As a complex radiance of the Universe the psychic energy glows with fires. This can be called Atma - the highest principle. (AY, 517)
The rise and fall of psychic energy is conditioned by various causes. The most important factor must be understood to be the actual quality of spirit of the bearer of psychic energy. As for the fiery spirit, even during the largest decline of psychic energy, its store is never completely exhausted. But the earthly spirit is affirmed only by the lowest energies, which very easily swallow up small stores of psychic energy; since this higher Fire is brought forth by the tension of the higher centers, by higher aspirations and higher feelings. The manifestation of psychic energy is, as it were, crystallized during a decline, but the fiery spirit is able to inflame these crystals by heart tension. A transport of the spirit can even manifest the potential of the store of psychic energy. Therefore the fiery spirit cannot exhaust its store of psychic energy. This store can burst ablaze during an inflammation of the centers. It can practically disappear during expenditure in battles and during sendings at far distances, but this sacred crystal cannot entirely disappear. Its action only alters its rhythm and its properties, as well as its tension. (FW III, 399)
The Spirit which realizes in life the power of tension of psychic energy can count upon the strength of psychic energy also during the crossing into the Subtle World. Our subtle body is fed by these saturations, and the fluids of psychic energy form the subtle body. Indeed, through transmutation of the centers psychic energy acts increasingly strongly, and the centers gather these powerful fluids for strengthening of the subtle body. When psychic energy is accumulated by exalted feelings, the transmutation of the subtle body is correspondingly saturated with fiery energies. Thus, it is important to intensify one’s forces in a fixed understanding of the power of psychic energy. The action of fiery energy intensifies all the succeeding manifestations of life " (FW III, 415)
Psychic energy penetrates all tissues, establishing equilibrium throughout the organism. During sickness psychic energy flows away from a certain center, weakening the function of the glands. Psychic energy is then impelled to those centers which are able to support and maintain equilibrium " (FW III, 416)
The Fiery World has its expression under the name of Psychic Energy. (FW III, 440)
We call psychic energy ‘eternally growing’. It can draw its own growth from out of Infinity. The only indispensible conditions are its realization, and its direction toward good. Without realization, the energy remains captive " (AUM, 472)
We also call psychic energy the ‘bulwark of self-sacrifice’. Of its might achievements are born. The feeling of ecstasy cannot be experienced without psychic energy " (AUM, 473)
Psychic energy is also called ‘a magnet’, and in such a definition there is much truth. Of course, the law of attraction and repulsion reacts especially upon psychic energy " (AUM, 474)
We also call the same energy ‘justice’. Since through the reaction of the energy, it is possible to determine the different qualities of people, it surely will be the path of justice " (AUM, 475)
We also call psychic energy ‘indefatigable’. True, the human organism can become wearied from the tension of the energy, but the energy itself is inexhaustible. Such a quality in the energy points to a cosmic source. The energy cannot be exhausted either by age or by illness. It may become silent if it is not summoned to action " (AUM, 476)
We also call the energy ‘labor’. In continuous conscious striving the energy acquires discipline. Awareness of labor is the basis of development of consciousness, that is to say, the beginning of the action of psychic energy. It is a mistake to think that a single tension will already bring the energy into motion. (AUM, 477)
Since aspiration is connected with psychic energy, then beauty also lies at the same source. Therefore I say that psychic energy is ‘beauty’. Thus one can enumerate all the qualities of the great energy, but as it is combined with all the manifestations of life, then it is correct to call it omnipresent and fundamental. Therefore, let us so call it. (AUM, 478)
Psychic energy is called the organ of the 4th dimension. (BR, 36)
see also Rhumkorf’s Coil

This definition is in context to Classic Yoga. See more contextual defintions for Psychic Energy.