noun which may take the genitive case particle 'no', noun
Indicates the first in a sequence, rank, or order. Often used with の to modify nouns.
He got the top grades in the class.
第一印象はとても大切だ。
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.
健康が第一だ。
Health is the most important thing.
安全を第一に考えてください。
Please put safety first.
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'.
第一、お金がないから旅行には行けない。
To begin with, I can't go on a trip because I don't have money.
第一、彼はまだ子供だ。
First of all, he's still a child.
You should consider your health as the top priority.
First of all, the budget isn't enough.
Family comes before work; family is the most important thing.
第一 casually means 'number one' or 'most important', while 最優先 is the more formal term used for explicit prioritization decisions.
第一 is used to list the most important point first among several, while そもそも is used to step back and question or restate the basic premise of the whole matter.
primary significance; first principle; most important thing · absolute truth; ultimate truth
first impression