Nephesh ha-Chaim 1:15 (here the author explains why the parts of the soul are called nephesh, ruach and neshamah respectively):
One might wonder that indeed the meaning of the term ‘neshamah’ (soul) is ‘breath’ (neshimah), and it appears that man’s breath is the air that rises from the chest, from below to above… and is not a higher order phenomenon. However, the reason the soul is described as breath is not as a reference to the breath of man, but rather, as it were, the breath of G-d, as it is written, ‘He blew into his nostrils the soul of life (‘nishmath chayim’).’
Our Sages of Blessed Memory compared the imbuing of the spirit of life into man to the fashioning of a glass vessel… When one contemplates the breathing of the mouth of the artisan into the glass vessel as he fashions it, one finds the process comprised of three stages. The first stage is as the breath of air is yet in the artisan’s mouth before it enters into the hollow tube. At that stage, it can only be called ‘breath’ (neshimah). The second stage is as the air enters into the tube and proceeds as a stream. Then it is called wind (‘ruach’). The third, lowest stage is as the wind exits the tube into the glass and spreads inside it until it becomes a vessel according to the will of the glassmaker. Then he ends the flow of wind. It is then called ‘nephesh,’ a term of cessation and rest.
This comparison illustrates the matter of the three faculties of the soul which flow, so to speak, from the breath of G-d’s mouth. The faculty of the nephesh is the lowest faculty, contained entirely within the body of man. The faculty of ruach comes via a flow from above; its upper extremity is bound to and held up by the lower facet of the neshamah and flows downward, entering also into the body of man, becoming bound there with the upper facet of the nephesh.