Oracle-bone script depicted two wooden panels of a double door side by side. The modern character 门 (simplified) retains that twin-panel silhouette, while the traditional form 門 makes the two planks even more visible. The character also serves as the Kangxi radical #169, appearing in dozens of related characters such as 间 (jiān, space/room), 问 (wèn, to ask), and 闻 (wén, to hear/smell) — all things that happen around or through a doorway.

Doors carry deep symbolic weight in Chinese culture. Red double doors (红门) on traditional homes ward off evil spirits, and door gods (门神, ménshen) — painted deities flanking the entrance — are a staple of Lunar New Year decoration. The phrase 登堂入室 ("enter the hall, enter the room") metaphorically means to reach a high level of mastery, reflecting how crossing thresholds signals progression. 门 is also a versatile measure word: 一门课 (yī mén kè) means "one course/subject," and 一门大炮 (yī mén dàpào) means "one cannon."