凹 āo concave
concave; hollow; sunken
How it came to be
The outline of a shape with its middle sunk down below the two sides: a dip, a hollow. Turned the other way up, it bulges out.
How it is used
- Concave - sunken/hollowed in - 凹陷 (āoxiàn) to cave in, 凹槽 (āocáo) a groove.
- Opposite of 凸 (tū, convex); together 凹凸不平 (āotū bùpíng) means bumpy/uneven.
- Also a pictograph - the character itself dips inward. Watch the reading: āo, not wā.