How to Write 凹 (āo/wā) — Meaning “Concave; sunken”

Imagine the character 凹 looks like a shallow bowl or a dent in a flat surface. The top line is the flat edge, and the sides curve inward to form a concave dip, just like a small valley or a sunken area.

Write 凹 with 5 strokes: first the left vertical, then top horizontal, then right vertical, then the inner horizontal stroke, and finally the bottom horizontal that closes the shape. A common mistake is making the inner stroke too flat; it should curve downward to show the sunken center.

凹 means "concave" with a sunken center, while 凸 means "convex" with a raised center — they are opposites in shape. 凶 means "fierce" or "ominous" and has a different inner component (乂, like an X), so it does not depict a sunken or raised shape at all.

凹 appears in technical terms like 凹陷 (āo xiàn, to sink in) and 凹凸 (āo tū, bumpy or uneven). It is also used in physics for 凹透镜 (concave lens). Though not common in daily conversation, it is essential for describing shapes, surfaces, and optics in Chinese.

Common words containing 凹 include: 凹陷 (āo xiàn) — To sink in; hollowed out; 凹透镜 (āo tòu jìng) — Concave lens; 凹凸 (āo tū) — Bumpy; uneven (concave and convex).