一つには時間がないし、二つにはお金もない。
For one thing, I don't have time, and for another, I don't have money.
noun
(not) even one
Used with a negative verb to mean 'not even one'; emphasizes complete absence.
彼は一つも間違えなかった。
He didn't make even one mistake.
noun, adverb
Adverbial use suggesting a casual attempt or small degree; often with ~してみる or ~してごらん.
一つ試しにやってみよう。
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~.
これは一つの解決策だ。
This is one kind of solution.