noun
the Boar; the Pig (12th Chinese zodiac sign)
Refers to the twelfth sign of the Chinese zodiac. In Japanese, the animal is usually called いのしし (wild boar), but 亥 is the zodiac name.
来年は亥年です。
Next year is the Year of the Boar.
noun
hour of the Boar (around 10 p.m.)
Obsolete temporal unit in the traditional Chinese time system, corresponding roughly to 9–11 p.m. or 10 p.m. to midnight. Used in historical contexts.
See also: 亥の刻
江戸時代には亥の刻に門が閉まった。
In the Edo period, the gates closed at the hour of the Boar.
noun
north-northwest
Obsolete directional term from the traditional Chinese zodiac compass points. Rarely used outside historical or divinatory contexts.
古い地図では亥の方角が北北西を示している。
On old maps, the direction of the Boar indicates north-northwest.
noun
tenth month of the lunar calendar
Obsolete month name in the traditional lunar calendar. Now only encountered in historical or literary texts.
旧暦の亥の月は今の十月ごろにあたる。
The Boar month of the old lunar calendar corresponds roughly to October now.
いのしし is the common word for 'wild boar' as an animal. 亥 is the zodiac sign name and is not used for the animal itself.
亥年 specifically means 'Year of the Boar'. 亥 alone is the sign itself.
The kanji 亥 is a Chinese zodiac character adopted into Japanese for calendrical and directional systems. The reading い is the Sino-Japanese on'yomi.