星期天
Xīng qī tiān · HSK 1
Sunday
☀️ 星期 = week + 天 (day) — the 'sun day' of the week
星期 means week (星 star + 期 period). 天 means day or sky. Together 星期天 literally reads as week-day-sky, the Sunday slot. Mandarin also uses 星期日 (rì = sun) for the same day.
期 — 其 (phonetic) + 月 (moon/time)
期 is a phono-semantic compound. The right side 月 (moon) signals meaning, since lunar cycles marked fixed time periods in ancient China. The left side 其 supplies the sound. Together it points to a set time, period, or appointed date — meanings still carried today in words like 期间 and 日期.
天 — 一 (one/sky) above 大 (big person)
Originally a pictograph of a person (大) with an emphasized head, representing what is above — the sky or heavens. The top stroke evolved into 一, symbolizing the vast expanse overhead. From 'sky' it extended to mean 'day,' 'heaven,' and 'nature.'