having a single eye; a one-eyed being (often used for mythical creatures).
昔話には一つ目小僧のような一つ目の妖怪が登場する。
Folktales feature one-eyed monsters like the 'hitotsume kozō'.
絵本の主人公は一つ目の怪物だったが性格は優しかった。
The picture-book protagonist was a one-eyed creature, but had a gentle personality.
the first in a series; the initial one (e.g., the first corner, the first item).
一つ目の角を右に曲がってください。
Turn right at the first corner.
会議の一つ目の議題は予算案です。
The first agenda item of the meeting is the budget proposal.
これが一つ目の課題なので、まずここから取り組もう。
This is the first task, so let's start with this.