一
yī
In real, traceable use. Part of the curated seed collection; community review is coming.
The number one; before a measure word also 'a, an'. 一个人 is 'one person' or 'a person', 一本书 'a book'. In speech its tone shifts — yí before a fourth tone (一个 yí ge), yì before the other tones (一天 yì tiān) — though dictionaries always write yī.
Số một; đứng trước lượng từ thì là “một” như trong “một người”, “một quyển sách”. Ví dụ: 一个人, 一本书. Khi nói, thanh điệu của 一 thay đổi: đọc yí trước thanh 4 (一个 yí ge), đọc yì trước các thanh khác (一天 yì tiān); từ điển vẫn ghi yī.
NumeralRegister: neutral
Examples
Editorial example (illustrative, not a corpus attestation) — awaiting a native-speaker check
Sources & notes
Hán-Việt bridge batch 063 (2026-11-14). Headword, Traditional form and pinyin checked against CC-CEDICT (CC BY-SA 4.0) source ↗ · Hán-Việt reading: Unihan kVietnamese source ↗ · No Vietnamese entry is linked as its twin; the Hán-Việt reading is given character by character. Definition, literal gloss and example sentence are original; the example has not had a native-speaker check yet.
Common questions
What does “一” mean?
The number one; before a measure word also 'a, an'. 一个人 is 'one person' or 'a person', 一本书 'a book'. In speech its tone shifts — yí before a fourth tone (一个 yí ge), yì before the other tones (一天 yì tiān) — though dictionaries always write yī.
Is “一” formal or informal?
一 is generally neutral.