同一

• Reading: どういつ
• Romaji: douitsu
• Kanji breakdown: 同 (dou) — same, similar; 一 (itsu/ichi) — one
• Pronunciation: /do.ɯ.i.t͡sɯ/

Meaning

Identical; the same; one and the same. Used to indicate complete sameness between two things.

A no-adjective and na-adjective used in formal and written contexts to assert that two things are exactly the same. Common patterns: 同一人物 (the same person), 同一の条件 (identical conditions). More formal than 同じ (onaji). Frequently appears in legal, academic, and investigative contexts.

Examples

1. 警察はこの二つの事件が同一犯だと見ている。 The police believe these two cases were committed by the same perpetrator.
2. 同一の商品でも店によって値段が違う。 Even the same product can have different prices depending on the store.
3. 彼と犯人が同一人物だとは信じられない。 I can't believe he and the criminal are the same person.

Usage Guide

Context: legal, academic, investigation

Tone: analytical

Origin & History

Compound of 同 (dou, same) and 一 (itsu, one). Together, 'same-one' — completely identical, not merely similar.

Cultural Context

Era: Classical

Generation: All ages

Social background: Universal