一つ
Meanings
Basic numeral; used for counting one item.
Please give me one apple.
for one thing
Used in itemized lists or when giving a first reason; often followed by 二つ目, etc.
For one thing, I don't have time, and for another, I don't have money.
Follows a noun to emphasize limitation; often used with だけ or しか.
Only one is left.
(not) even one
Used with a negative verb to mean 'not even one'; emphasizes complete absence.
He didn't make even one mistake.
Adverbial use suggesting a casual attempt or small degree; often with ～してみる or ～してごらん.
Let's just give it a try.
noun which may take the genitive case particle 'no'
some kind of; one type of
Used as a no-adjective to indicate a certain unspecified kind; often in 一つの～.
This is one kind of solution.
Usage patterns
- 〈物〉を一つくださいplease give me one ~
Please give me one apple.
- 一つには〈事〉for one thing, ~ (used when listing reasons)
For one thing, it's because there's no time.
- 〈物〉が一つしかないthere is only one ~
There's only one wallet in this bag.
- 〈物〉一つ〈動詞〉ないnot even one ~ (does something)
He doesn't tell even a single lie.
- 一つ〈動詞〉てみるjust try doing ~
Let's just give it a try.
- 一つの〈事〉a certain kind of ~; one form of ~
This too is one way of thinking about it.