The characters `礼拜 (lǐbài)` combine to mean “to worship” or “a religious service,” a term that became associated with the Christian weekly service. When you add the number `一 (yī)`, it signifies the first day *after* the day of worship (Sunday, or `礼拜天`). Therefore, 礼拜一 is the first day of the work week.
The existence of `礼拜一` is a fascinating linguistic footprint of Western cultural influence in China. The `礼拜 (lǐbài)` system for naming the days of the week was introduced by Christian missionaries. `礼拜天 (lǐbàitiān)` or `礼拜日 (lǐbàirì)` was Sunday, the “day of worship.” The subsequent days were then numbered one through six. This contrasts with the most common system, `星期 (xīngqī)`, which means “star period” and has origins in ancient astronomy. It also differs from `周 (zhōu)`, meaning “cycle,” which is often used in more formal or written contexts. While in English, “Monday” has pagan origins (named after the Moon), the Chinese term `礼拜一` has a clear, relatively modern religious source. This highlights how modern Mandarin has incorporated different cultural frameworks to describe the same concept. Using `礼拜一` can sometimes subtly indicate a regional background (southern) or familiarity with Christian culture, though for most speakers, it's just a neutral synonym for Monday.