The kanji character 昨 primarily means "yesterday" or "the previous day." It refers to the day immediately preceding the current day. This core meaning is central to all its uses.

・On-yomi (音読み): sa(ku) ・Kun-yomi (訓読み): None, as the meaning is primarily expressed through the On-yomi.

⚫︎ 昨日（きのう） Translation: Yesterday ⚫︎ 昨夜（さくや） Translation: Last night ⚫︎ 昨年（さくねん） Translation: Last year

The kanji 昨 is a phono-semantic compound (形声文字, keisei moji) consisting of two parts: The left side is the radical of "sun/day" (日, hi), indicating that it has to do with time. The right side is "乍", which provides the phonetic component, indicating the pronunciation "sa(ku)". Together, they depict "the previous day".