一定
yī dìng
In real, traceable use. Part of the curated seed collection; community review is coming.
Certainly, definitely, without fail. It goes before the verb: 我一定来 'I will definitely come'. The negative 不一定 means 'not necessarily'. Before a noun, with 的, it means 'a certain (amount of)': 一定的时间 'a certain amount of time'.
Nhất định, chắc chắn, thế nào cũng. Đứng trước động từ: 我一定来 (tôi nhất định sẽ đến). Dạng phủ định 不一定 nghĩa là “chưa chắc, không hẳn”. Đứng trước danh từ, có 的, thì nghĩa là “nhất định, nào đó”: 一定的时间 (một thời gian nhất định).
AdverbRegister: 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 ↗ · Vietnamese cognate: Idiomer entry “nhất định” (nhat-dinh). Definition, literal gloss and example sentence are original; the example has not had a native-speaker check yet.
Equivalents & related
Common questions
What does “一定” mean?
Certainly, definitely, without fail. It goes before the verb: 我一定来 'I will definitely come'. The negative 不一定 means 'not necessarily'. Before a noun, with 的, it means 'a certain (amount of)': 一定的时间 'a certain amount of time'.
Is “一定” formal or informal?
一定 is generally neutral.