一つ
1
numeric
one
１つが通り過ぎたかと思うと、すぐに次の台風が接近する。
No sooner has one typhoon passed than the next one approaches.
2
for one thing
often used in itemized lists
一つには、私は貧しいし、それにまた忙しくもある。
For one thing, I am poor; for another, I am busy.
3
only
after a noun
4
(not) even
with a verb in negative form
妻の死の知らせを聞いてもまゆ一つ動かさなかった。
He did not even raise an eyebrow at the news of his wife's death.
5
just (e.g. "just try it")
6
some kind of;one type of
Other forms
１つ 【ひとつ】 · 一 【ひとつ】 (irregular okurigana usage)