Hai

It began as one marker in a twelve-part time cycle. The cycle later called the Earthly Branches appears in Shang divination inscriptions from roughly 1300–1050 BCE. Those Shang divination inscriptions place calendar notation inside divination and ancestral ritual; they name no single inventor of an isolated 亥 glyph.

The system links 亥 to the other eleven branches and to the ten Heavenly Stems. Read pairings such as 己亥 as one calendrical date label, not as two everyday words side by side.

What does 亥 mean in Chinese and Japanese?

Chinese and Japanese traditions attach different animal words to 亥. Chinese usage pairs it with pig; Japanese dictionaries give イノシシ, wild boar, read い. The branch position is identical, so this is a regional animal label, not a different character.

The same branch can mark the end of the cycle, a late-evening slot around 9–11 p.m. called 亥時, the north-northwest direction, or the tenth lunar month, 亥月. Japanese calendrical language also uses 戌亥 for the northwest sector between 戌 and 亥.

亥 and 豕 are easy to mix up

Check the neighbors before you translate 亥 as “pig.” Classical Chinese and Japanese reference works record 亥豕 as a set phrase for copying or printing errors caused by similar forms. If someone sends lone 亥, ask which date, zodiac, or text they mean; “calendrical or textual reference” beats “pig emoji” every time.