The almanac is the household reference for what to do when. Which days suit a wedding, a move, a funeral, opening a business, cutting hair. It has been printed continuously for centuries and you can still buy one in Hong Kong, a fat cheap paperback with a red cover.
Its proper name was 通書 — the comprehensive book.
The trouble is 書, syu1. It is a perfect homophone of 輸, syu1, to lose.
So the book of auspicious days, which exists entirely to help you avoid bad luck, was carrying a word that sounded like losing every time anyone said its name. It was renamed. Not translated, not abbreviated — swapped for its opposite. The comprehensive book became the comprehensive win.
Why this is the section’s keystone
Because it shows the mechanism operating on itself. Everywhere else, substitution happens to ordinary things: pig’s tongue 豬舌 becomes 豬脷 because 舌 sounds like 蝕, to lose money. An empty flat is advertised as 吉屋, lucky house, because the honest word 空 hung sounds like 凶, ominous. A vacancy that cannot be described as empty.
Here the same rule reaches the reference work that documents the rule, and the reference work submits. There is no authority above it to appeal to. The almanac cannot look up whether it should rename itself; it just has to.
One honest note
The homophony is not uniquely Cantonese — 書 and 輸 collide in Mandarin too, both shū. What is Cantonese is that the south actually renamed the book. In the north it stayed the old name or became 黃曆, the yellow calendar. Only here did the collision get treated as a problem serious enough to fix.
That’s the useful distinction for this collection generally. The raw material — characters, sounds, coincidences — is often shared. What differs is how far a culture is prepared to go about it.