Well, when I talk to my Chiropractor (who also trains with me) about the kua he calls that the inguinal fold and inguinal canal area. FWIW.
Yes, I have heard the word used that way. I don't know if clarity here is a simple matter of a word from a Chinese language native or a matter for a conference between Chinese speaking martial artists, English speaking martial artists, and at least a handful of martial artists that speak both languages.
I came across an article some time ago that I was able to track down in my notes. I don't know where I got it from. A quick search of the title yields the following website:
A cursory glance suggests that the material is the same.
Anyway, here is a bit taken from an article titled:
Function and Usage of the kua
Q & A with Chen Zhonghua
This article presents questions and answers, based on instructions in workshops, with Chen Zhonghua. The course material was Hong's Practical Method of Chen style Tai Chi. Training emphasized mechanics and application skills. This selection of those questions and answers dealt with understanding of function and usage of the kua,in developing those skills....
Anatomy and General Understanding
Q. It is quite common for teachers of the internal arts to emphasize the importance of the kua for attainment of higher levels of skill. What could you say about the kua in terms of its role in the practice of Tai Chi?
Its fundamental role is that without the kua the upper and lower body cannot properly work together. The kua is the body part responsible for integration of upper and lower body.
Q. Can you give some description or details? In context of the hips, groin, pelvic girdle, or the femur, speaking in simple layman's view of anatomy—- how would you describe the kua?
The kua is that ball joint inside, at the top of the thigh bone. I dont know the English name for it (femur), the ball joint inside, inside the hip.
Q. The tops of the thigh bones that rotate?
Yes, the ball joint, thats the kua.
The rest, the body parts connected with it, are just things associated with it. Thats why there is always confusion, why the understanding of it always changes. At different levels you will be able to associate your kua with other parts of your body. Its these various different perceptions of experience of the kua, that give rise to different explanations of the kua among different masters or teachers.
Q. When they talk about the kua, maybe their definitions are more in terms of its usage?
Yes. As you exercise that joint, itaffects the structure and movement of your body. The better you are at using the kua, the better your body is coordinated. So it will appear that different masters use the kua differently, with varying levels and depth of experience of that function.. Ability to connect the kua with better integration with the body reveals higher skill.
But the simple objective anatomical definition of the kua has not been wrong in the past. It is commonly understood to be that ball joint.
I can't vouch for the veracity of this or of the article as a whole but I'm pretty sure it is worth reading and considering.
Now whether this has to do with the mind/body connections of Japanese martial arts I do not know. But, I'd like to.