Unless (conjunction)

1. If not; except on the condition that.
2. Except in the event that.

Origin:

Old english, from un- "not" + licgan "lie, be the case".

Examples:

1. You won't pass the exam unless you study.
2. I will be late unless I leave now.
3. I won't go to the party unless you come with me.
4. We will not be able to complete the project unless we work together.
5. I will not lend him the money unless he pays me back.