Chōonpu

Definition:

Chōonpu (長音符, literally “long sound mark”) is the horizontal dash (ー) used in katakana to indicate a long vowel — extending the preceding vowel by one mora. For example, カ (ka) + ー = カー (kaa). It is the standard way to mark vowel length in katakana and is essential for correctly reading and writing loanwords in Japanese.

In-Depth Explanation

Basic function:

Where it appears:

The chōonpu is used almost exclusively in katakana for:

• Loanwords: コーヒー (koohii, coffee), ケーキ (keeki, cake), ビール (biiru, beer)
• Foreign names: マーク (maaku, Mark), サラー (saraa, Sarah)
• Onomatopoeia in katakana: ガーン (gaan, shock sound), ドーン (doon, boom)

Why not in hiragana?

Hiragana marks long vowels differently — by adding the appropriate vowel kana:

• おかあさん (okaasan, mother) — long /a/ written with extra あ
• おにいさん (oniisan, older brother) — long /i/ written with extra い
• くうき (kuuki, air) — long /u/ written with extra う
• おねえさん (oneesan, older sister) — long /e/ with extra え (or sometimes い)
• おとうさん (otousan, father) — long /o/ typically written with う

The chōonpu (ー) is occasionally used in hiragana in informal writing (e.g., そーだ for そうだ) but this is non-standard and considered casual.

Vertical vs. horizontal writing:

In vertical text (縦書き, tategaki), the chōonpu is written as a vertical line (｜) rather than horizontal. This follows the text direction.

Common learner mistakes:

• Forgetting the chōonpu and shortening the vowel: ビル (biru, building) vs. ビール (biiru, beer) — these are different words
• Using it in hiragana text (non-standard)
• Confusing it with the kanji for “one” (一) in handwriting

Related Terms

• Katakana
• Mora
• Small Tsu
• Vowel Length

See Also

• Japanese Writing System
• Sakubo

Research

• Irwin, M. (2011). Loanwords in Japanese. John Benjamins. — Analyzes how loanword adaptation uses katakana conventions including the chōonpu.
• Vance, T. J. (2008). The Sounds of Japanese. Cambridge University Press. — Phonological analysis of vowel length contrasts in Japanese.