‘一旬’ literally means ‘one xún’, where ‘一’ is the numeral ‘one’ and ‘旬’ is an ancient Chinese unit of time equal to ten days. Historically, the lunar month was divided into three xún: the first (shàngxún), middle (zhōngxún), and last (xiàxún) ten-day periods. This usage remains common in formal writing, weather reports, and agricultural or administrative contexts when referring to short-term time spans.

In literary or historical contexts, ‘旬’ can also mean ‘ten years’, so ‘一旬’ may occasionally signify a decade—especially in poetic or biographical language (e.g., ‘年过七旬’ meaning ‘over seventy years old’). However, this decade sense is almost always used with age or lifespan and rarely stands alone without context. The ten-day meaning is by far the dominant and most practical usage for learners.