A power of vital nature. If fierce and hostile, it may be a form of an adverse force.
The hostile forces exist and have been known to yogic experience ever since the days of the Veda and Zoroaster in Asia (and the mysteries of Egypt and the Cabbala) and in Europe also from old times. These things, of course, cannot be felt or known so long as one lives in the ordinary mind and its ideas and perceptions; for there, there are only two categories of influences recognisable, the ideas and feelings and actions of oneself and others and the play of environmental and physical forces. But once one begins to experience that all is an action of forces, forces of Prakriti (Nature) psychological as well as physical, which play upon our nature -- and these are conscious forces or are supported by a consciousness or consciousness behind. One is in the midst of a big universal working and it is impossible any longer to explain everything as the result of one's own sole and independent personality. Those who have developed the inner view of things on the vital plane have plenty of experience of the hostile forces.