昨 is built from the 日 and 乍 (suddenly (in 作·昨)) components.
It belongs to a phonetic family with 作, 酢, and 搾 — they share the 乍 component and the reading サク.
A common word using 昨 is 一昨日 (おととい), meaning “the day before yesterday”.
Kanji that look similar include 冒, 厚, 指, and 星.
