WAKAN is whatever conforms integrally to its proper “genius”; the Principle is WAKAN-Tanka, namely: what is absolutely “Self”; on the other hand a sage is he who is wholly in conformity with his “genius” or with his “essence,” with that which is none other than the “Great Spirit” or the “Great Mystery.” WAKAN is what enables us to apprehend directly the Divine Reality; a man is wakan when his soul manifests the Divine with the spontaneous and flashing evidence of the wonders of Nature. (GTUFS: FSun, The Sacred Pipe)
WAKAN-Tanka: The name WAKAN-Tanka, literally “Great Sacred” (wakan = sacred) is commonly translated “Great Spirit” or “Great Mystery,” and has also been rendered as “Great Powers,” the plural being justified in view of the polysynthetic significance of the concept. (GTUFS: FSun, The Shamanism of the Red Indians)
Objections are sometimes raised to the name “Great Spirit” as a translation of the Sioux word WAKAN-Tanka, and of similar terms in other Indian languages; but although WAKAN-Tanka (and the terms which correspond to it) can also be translated by “Great Mystery” or “Great Mysterious Power” (or even “Great Medicine”), and although “Great Spirit” is no doubt not absolutely adequate, it nonetheless serves quite well enough and in any case conveys the meaning in question better than any other term; it is true that the word “spirit” is rather indefinite, but it has for that very reason the advantage of implying no restriction, and this is exactly what the “polysynthetic” term WAKAN requires. The expression “Great Mystery” which has been suggested by some as a translation of WAKAN-Tanka (or of the analogous terms, such as Wakonda or Manitu, in other Indian languages) is no better than “Great Spirit” at expressing the idea in question: besides, what matters is not whether the term corresponds exactly to what we mean by “Spirit,” but whether the ideas expressed by the Red Indian term may be translated by “Spirit” or not. (GTUFS: FSun, The Sacred Pipe)