凹
Character Story & Explanation
In daily life, 凹 most commonly appears in technical, descriptive, and colloquial contexts—not as a verb but as an adjective or noun. It's standard in physics textbooks (e.g., 凹透镜 āo tòujìng, 'concave lens'), industrial design manuals, and metrology reports measuring surface irregularities. A well-documented phrase is 凹凸不平 (āo tū bù píng), meaning 'uneven/rough surface', used in construction standards and road safety bulletins since the 1950s. In internet slang since ~2015, 凹 has been adopted alongside 凸 (tū, 'convex') to humorously represent emotional states: 凹 = feeling down, 凸 = hyped up—echoing their visual opposites.
凹 is a pictograph with documented origin: oracle bone and bronze inscriptions show it as a simplified outline of a concave basin or depression in terrain—two side lines curving inward, capped and base-lined. Its earliest confirmed use (Shang dynasty divination records) denotes 'sunken landform', consistent with its modern meaning. No speculative etymology needed—it’s one of Chinese writing’s clearest visual metaphors.
Imagine walking through Beijing’s historic Hutong alleys on a rainy afternoon. You pause beneath a worn gray brick archway—its stone surface deeply worn by centuries of rain and footsteps. The center of the arch dips inward, forming a smooth, curved hollow—a perfect real-world '凹' (āo). This character visually mirrors that sunken curve: its shape is literally a downward indentation, like a bowl’s interior or a fingerprint’s depression. It’s not just abstract—it’s tactile, architectural, geological.
In modern China, 凹 appears everywhere you notice depth: in engineering blueprints specifying lens curvature, in smartphone screen specs ('curved凹display'), and even in slang. Young people jokingly say '我凹了' (wǒ āo le) meaning 'I’ve sunk into despair'—a playful, self-deprecating twist on its literal sense of depression. Though rare as a standalone word, its presence is structural—like the hollow in a clay teacup that makes it hold liquid.
The character’s radical 凵 (kǎn), meaning 'open container' or 'hollow', anchors its semantic core—anything that opens downward or caves in. Its five strokes are deceptively simple: a top horizontal line, then two downward curves framing an inward dip, followed by a closing base stroke. Unlike many HSK 6 characters burdened with obscure literary usage, 凹 remains grounded in physical reality—whether describing a crater on the moon (lunar 'concave basins'), a dent in a car fender, or the subtle hollow behind a dancer’s collarbone captured in a portrait.
Example Sentences
Common Compounds
Similar Characters — Don't Mix These Up
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