JimmySeal wrote:

I can't find any evidence of this word being used in Japanese, though it looks to be fairly common in Chinese.  It could be that it was used at one time and has since been replaced with the Anglo loanword ジグザグ.

Why put a non-word in chapter 1?  To scare away the faint of heart.  Only those that be brave enough to conquer chapter 1 may continue on ...

JimmySeal wrote:

The word may have been in use when RTK2 was originally published.  I can't say for sure.

I reckon he had to make a stretch for that character because there are little or no compounds that actually contain that character.  It doesn't have much meaning on its own and is mostly used as an old-timey way of writing the possessive particle の.
In fact, 之字形 just means "shape that looks like 之".  And yet he included it in RTK1 before he had any intention of writing RTK2, so I guess he was obliged to include something for it.  So that's why.

I guess I'll just go with it then. Though, doesn't he realize how discouraging the phrase "rare reading" is when put beside a kanji in chapter 1.  There are oh so many common readings that could be learned first. 

Forgive my ranting.

KMDES wrote:

The reason is doesn't pop up is because it's 2 words. 之 and 字形.

If it was a common compound it would be in a dictionary regardless.

Did you really just use a comparison to an English dictionary? Pretty sure Japanese isn't English.

Common JAPANESE compounds are in larger dictionaries. Google it if you like and see that it isn't really a Japanese word. There are 426 matches for it on Japanese domains, all of which seem to be talking about Chinese or proper nouns (based on a cursory look).

You can coin a compound and it would make sense, but the point is that it isn't used in Japanese.