Vajra means thunderbolt or diamond (vaj, hard; ra, wedge).
The thunderbolt of the Indra is called vajra; yogini means female consort, a divine being that appears as a consort, the yoked one; shrî means holy and mahâ large; mâyâ is the Shakti, the feminine being that emanates from the masculine creator god and represents the world, a sort of mother of the world, a building material, a material—the word “materia” belongs here—of the visible god, but different from god inasmuch as it depicts his femininity.
This femininity is called world. We speak of mother earth or even madam world; shrî mahâmâyâ is therefore the holy great illusion or also the great reality that is also an illusion; Târâ is a specific Mahâyâna goddess. ~Carl Jung, Psychology of Yoga and Meditation, Page 63-64
Sattva, i.e., an entity, a being. This term belongs to the three so-called gunas but I will spare you all that.
This Buddha has as an epithet the name vajra sattva which means diamond being or thunderbolt being.
I prefer the first meaning. It is on the primitive level of the Bon that the thunderbolt is important as a magic missile, but later on a higher philosophical level the diamond meaning plays a much greater role: as the enduring, hardest being that is not subject to change.
For example, in Chinese philosophical yoga it describes it as the subtle body, the spiritual body, which is no longer subjected to any changes.
There this vajra takes on absolutely the meaning of the lapis philosophorum, the philosophers’ stone, that eternal being brought forth from man, that arises from the striving of his life, from the laboratorium, and then somehow outlives it.
The body of the sleeping one is therefore the body of the Buddha vajra sattva—of the diamond being Buddha. Which is to say that this is a matter of a transformation of the body into the diamond being, this eternal, enduring thing. ~Carl Jung, Psychology of Yoga and Meditation, Page 66