第一(だいいち)に

第一(だいいち)に introduces the first and often most important point in a series. It is used in logical arguments, speeches, and essays.

Series pattern

Often used with sequential markers:

• 第一(だいいち)に (firstly)
• 第二(だいに)に (secondly)
• 第三(だいさん)に (thirdly)

WITHOUT に:
第一(だいいち) alone (without に) emphasizes priority: 健康(けんこう)第一(だいいち) (health first), 安全(あんぜん)第一(だいいち) (safety first).

Similar words

• まず: first, to begin with (more colloquial and versatile)
• 最初(さいしょ)に: at first, initially (temporal focus)
• 何(なに)よりも: above all else (strongest emphasis on priority)
• そもそも: in the first place (challenges premises, more confrontational)

Register

Neutral to formal. Common in structured arguments and formal writing. In casual speech, まず is preferred.