one day

Adverb

Japanese Meaning

将来のいつか：未特定の未来のある時点 / 過去のある日：特定されていない過去の時点

One day I hope to travel to every continent.

いつか私はすべての大陸を旅してみたいと思っています。

Sense（1）

(set phrase) At some unspecified time in the future.

One day I shall upgrade my software, but not just yet.

Sense（2）

At some unspecified time in the past.

One day I was playing with a girl from my class.

Sense（3）

Used other than figuratively or idiomatically: see one, day.

You can stay one day or two.