第一・第１|だいいちdaiichi[1]atamadaka (head-high)

1. no-adjectivefirst; foremost; number one
   まず、第だい一いちに名前なまえを書かきなさい。↗

   Write your name, first of all.
2. no-adjectivemost important
   健康けんこうが第だい一いちだ。↗

   Nothing is more important than health.
3. no-adjectivebest; greatest; most
   日本にっぽんは天下てんか第だい一いちの国くにである。↗

   Japan is the best country under the sun.
4. adverbabove all; besides; in any case; to begin with

• Synonym一番いちばんNeutralFirst or most, as in 「一番好き」; the everyday word for ranking, while 「第一」 is more formal and also means most important.
• SynonymトップNeutralLoanword for the top spot or the people at the top, as in 「トップに立つ」.
• SynonymベストNeutralLoanword for the best, stressing peak condition, as in 「ベストを尽くす」.
• SynonymナンバーワンNeutralLoanword for number one, the top name among many; heard mostly in advertising and promotion.
• Synonym一等いっとうNeutralFirst class or first prize, as in 「一等賞」; also used adverbially to mean most.
• Synonym一級いっきゅうNeutralFirst-class or first grade, as in 「一級品」 and 「一級建築士」.
• Synonym随一ずいいちWrittenWritten/formal prose for second to none, as in 「県内随一の名所」; 「第一」 can also refer to simple order.
• Synonym最初さいしょNeutralThe beginning or outset, focused on order in time, as in 「最初の日」.
• SynonymはじめにNeutralFirst of all, at the start, as in 「はじめに説明します」.
• Synonym真っ先まっさきNeutralThe very front or first, stressing position or time, as in 「真っ先に逃げる」 and 「真っ先に思い浮かぶ」.
• SynonymまずNeutralAdverb for first of all, before anything else, as in 「まず手を洗う」; common in speech.
• Synonymいの一番いのいちばんCasualColloquial for the very first thing, as in 「いの一番に駆けつける」; 「第一」 leans toward order and importance.
• Antonym最終さいしゅうNeutralFinal or last; the opposite of 「第一」.
• Antonym最後さいごNeutralThe end or the last; opposite of 「第一」's sense of coming first.

Use 「第一」 for first in order or most important, as in 「安全第一」 and 「第一印象」. In casual speech rank with 「一番」; for first in time say 「最初」 or 「真っ先」; for doing something first use 「まず」; for foremost of many, 「随一」 in formal prose. The opposite is 「最後」.

Usage comparisons are AI-assisted and cross-checked by multiple models; for study reference only

1. 序列じょれつが一番いちばん目めであること。最初さいしょ。
2. 最もっともすぐれていること。
3. 最もっとも重要じゅうようなこと。最優先さいゆうせん事項じこう。
4. まず、そもそも。