井 means “well”

い · i

Also: well crib, town, community

Kun'yomi (Japanese reading)
い
On'yomi (Chinese reading)
セイ, ショウ

JLPT N1 · Taught in grade 4 · 4 strokes

The story

Four logs laid in a square: the wooden frame around a well's mouth, seen from above. 井戸 is a well and 天井 the ceiling, 井 fills surnames like 井上 and 石井, and 市井, market and well, means ordinary street life.

Used in 井戸 (ido, well), 天井 (tenjou, ceiling), and 市井 (shisei, the streets/ordinary people)

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Readings from KANJIDIC2, © EDRDG, CC BY-SA.