1. Meaning and Usage
The core meaning of the kanji 凹 is "concave," "hollow," "sunken," or "to dent." It describes a surface that curves inward or a depressed area. It is the direct opposite of its counterpart, 凸 (convex).
Common Readings and Words:
おう (ō): The Sino-Japanese reading, used in compound words.
凹凸 (ōtotsu): Unevenness, concavity and convexity, bumps and dips.
凹面 (ōmen): Concave surface.
へこ (heko): Used in verbs.
凹む (hekomu): The basic verb meaning "to become dented," "to cave in," "to be depressed (emotionally)."
くぼ (kubo): Used in nouns and verbs.
凹み (kubomi): A hollow, a dent, a depression.
凹む (kubomu): An alternative reading for "to become hollow."
2. Correct Stroke Order
Writing 凹 correctly is unique because it is one of the few kanji that does not follow the standard "top-left to bottom-right" flow. Its stroke order is specific and must be memorized.
Total Strokes: 5
Step-by-Step Breakdown:
Stroke 1: Left vertical stroke. Write from top to bottom (竖).
Stroke 2: Top horizontal and right vertical in one continuous stroke. Start from the left, write the top horizontal, then turn and go down the right side (横折).
Stroke 3: The bottom horizontal stroke. Write from left to right, connecting the bottom of the left and right verticals (横).
Stroke 4: The top-left inner vertical stroke. Write from top to bottom (竖).
Stroke 5: The bottom-left inner horizontal stroke. Write from left to right (横).
Key Points:
The character is written by first creating the outer "container" (Strokes 1, 2, and 3), and then filling in the inner details.
This order ensures the character is symmetrical and properly enclosed.
3. Historical Origins and Etymology (The "Story" Behind the Kanji)
The kanji 凹 is a brilliant example of a 指事文字 (shiji moji) or ideographic character. This means it is a simple symbol that represents an abstract idea directly, rather than being composed of other meaningful parts.
The Origin:
凹 is a pictograph. It is a stylized drawing of a concave or sunken object.
If you look at the character, it visually represents a depression or a hollow space. The inner space is enclosed, and the sides curve inward, creating a clear image of a cavity.
This is one of the most intuitively designed kanji. Its form is its meaning. There is no complex historical evolution from other components—it was created specifically to depict the concept of "hollowness" or "concavity."
Its counterpart, 凸 (convex), was created in the same way, as a pictograph of a bulging or protruding shape.
4. Example Sentences
Here are some example sentences showing the different uses of 凹.
As a Verb "To Dent" (へこむ):
Romaji: Jiko de kuruma no doa ga hekonda.
English: The car door was dented in the accident.
事故で車のドアが凹んだ。
As a Noun "Hollow" (くぼみ):
Romaji: Jimen no kubomi ni mizu ga tamatta.
English: Water collected in a hollow in the ground.
地面の凹みに水がたまった。
In a Compound Word (おう):
Romaji: Kono renzu wa ō renzu da.
English: This lens is a concave lens.
このレンズは凹レンズだ。
Used Emotionally (Slang):
Romaji: Shiken ni shippai shite hekonde iru.
English: I failed the exam and I'm feeling down/depressed. (My spirits are "dented").
試験に失敗して凹んでいる。
Summary
Meaning: Concave, hollow, sunken, dented.
Writing: 5 strokes. A unique stroke order where the outer "container" is drawn first (left, top-right, bottom), followed by the inner strokes.
Origin: A pictographic character (指事文字). Its form is a direct, stylized drawing of a concave or sunken object, making its meaning instantly recognizable. It is a perfect example of a kanji where the shape itself tells the story.