ashva

http://www.swami-krishnananda.org/brdup/brhad_I-01.html

When the horse becomes the vehicle of the celestials, it is called 'Hayo'. When it becomes the vehicle of Gandharvas, demi-gods, above the earth, it is called 'Vājī', a peculiar name ascribed to the horse. When it becomes the vehicle of the demons, it becomes 'Arva'. It becomes the ordinary horse, Aśva, when it becomes the vehicle of human beings. The substance of all these things is the ocean. Here, the great commentator, Achārya Śankara tells us the ocean means the Cosmic Soul. It does not mean the ocean which is water. The Universal Soul is the basis of the world, as the horse is the basis of the entire sacrifice. It is the substratum; and every activity - name, form, action - is something like a wave in the ocean. But the wave is the ocean. The wave is in the ocean, or on the ocean, as you may think of it. Likewise, all actions, name and form, rise and subside within the bosom of the universal Soul, so that you may say, just as waves are the ocean, actions are the Universal Soul. So the universe is the ocean, or rather, the Universal Soul is the ocean. That is the deepest and the nearest associate. The greatest friend of man is God. That is what is intended here. And He is the support, ultimate resort and refuge - samudra evᾱsya bandhuḥ, samudro yoniḥ.