第だい一いち

noun which may take the genitive case particle 'no', noun

first; number one

Indicates the first in a sequence, rank, or order. Often used with の to modify nouns.

• 彼かれはクラスで第だい一いちの成せい績せきを取とった。

  He got the top grades in the class.

• 第だい一いち印いん象しょうはとても大たい切せつだ。

  First impressions are very important.

noun which may take the genitive case particle 'no', noun

most important; best; foremost

Emphasizes priority or supreme importance. Overlaps with sense 1 but focuses on qualitative primacy rather than numerical order.

• 健けん康こうが第だい一いちだ。

  Health is the most important thing.

• 安あん全ぜんを第だい一いちに考かんがえてください。

  Please put safety first.

adverb

first of all; to begin with; above all

Adverbial use, often at the start of a sentence or clause, to introduce a primary reason or point. Can also imply 'in the first place' or 'anyway'.

• 第だい一いち、お金かねがないから旅りょ行こうには行いけない。

  To begin with, I can't go on a trip because I don't have money.

• 第だい一いち、彼かれはまだ子こ供どもだ。

  First of all, he's still a child.