昨

Phono-semantic compound:

日 (날 일, “sun, day”) — semantic, indicating relation to time or day.

乍 (잠깐 작, “for a moment, suddenly”) — phonetic, providing the sound 작 and the sense of something that has just passed.

Originally referred to the day that has just passed, hence the meaning yesterday.

작일(昨日) — yesterday

작금(昨今) — literally “yesterday and today”; means nowadays, these days

작년(昨年) — last year, the previous year

작자(作者) — although written with the same phonetic component, here 작 means “to create,” not “yesterday” (different meaning)