Actually, that's a very good question.
From The Laws of Form by G. Spencer Brown:
"If a content is of value, a name can be taken to indicate this value. Thus the calling of the name can be identified with the value of the content."
We name things in order to be able to refer to them without having to explicitly state their characteristics and the nature of their interactions with other things in the world around them. If you are conversant in Special Relativity, I can jot down E=MC**2 and you will know that I'm referring to the fact that a given quantity of matter contains a potential amount of energy that's equal to the mass of the matter times the square of the speed of light in a vacuum.
So having explained the nature of the unification of mind and body via words, exercises and practical demonstrations, and named it ki, I can tell a student to "extend ki" and she will immediately know what I am looking for and how to do what I am asking her to do without me having to explain it every time.
OK, so the term ki/qi is just a label that represents a part of a process that leads to a specific physical result initiated by mind? If so, it appears to me to be a very appropriate transition or bridge from mental to physical