Sometime; at some unspecified time in the future.
"I hope to visit Paris someday when I have saved enough money."
In plain English: Someday means at an unspecified time in the future when something will eventually happen.
"Someday I want to travel around the world."
Usage: Use "someday" to refer to an indefinite point in the future, often implying hope or intention rather than a specific plan. It differs from "some day," which is rarely used as two separate words unless emphasizing distinct days within that timeframe.
The word someday originated from combining the words some and day. Over time, these two separate elements fused into a single term to express an unspecified point in the future.