2015年10月19日 · But in Chinese, 天 and 日 could be used for the meaning of day both. So the people started to say 星期天 instead of 星期日, and the original meaning (i.e. Sun) was lost, which would be a "misuse". Nowadays 星期日 and 星期天 are both correct. Basically in a formal context, such as in news, 星期日 is used more than 星期天.