T: 日 S: 日 [ri4] = 1. day 2. (formal) sun 3. Japan 4. Japanese
一年中白天最短的是十二月二十一日。
yi4 nian2 zhong1 bai2 tian1 zui4 duan3 de5 shi4 shi2 er4 yue4 er4 shi2 yi1 ri4.
The shortest day of the year is on December the 21st.
https://www.learnwitholiver.com/chinese/daily-sentence-3194