Though “some day” and “someday” sound alike, they are used in different contexts. “Some day” refers to a specific day, though the exact date may not be known. “Someday,” on the other hand, refers to an indefinite time in the future.
Some day
Definition:
“Some day” refers to a particular, but unspecified, day in the future. It implies that something will happen on a certain day, even if that day is not currently known.
Examples:
We all hope and pray that some day they are back together.
Some day, you will realize the importance of this decision.
I’d like to visit Paris some day when I have more time.
Someday
Definition:
“Someday” refers to an indefinite point in the future. It is used to express a general idea or hope about something happening eventually, without specifying when.
Examples:
No doubt, if we stay on this course, we’ll succeed someday.
Someday, I’ll write a book about my travels.
They dream of owning a house by the beach someday.
“Some day” refers to a specific day that is yet unknown, while “someday” refers to an indefinite future time. Being mindful of the distinction will help ensure clarity in writing and speech.