Inexplicable (adjective)

1. Not able to be explained or understood.
2. Not able to be accounted for or made clear.
3. Not able to be rationalized or justified.

Origin:

From in- ("not") + explicable.

Examples:

1. The phenomenon was inexplicable.
2. His behavior was inexplicable.
3. The accident was inexplicable.
4. The results were inexplicable.
5. The disappearance was inexplicable.