insoluble

That cannot be dissolved.

Difficult or impossible to solve or explain; insolvable.

That cannot be loosed or undone.

Not soluble; incapable of being dissolved.

Incapable of being solved or explained; not susceptible of solution or explanation.

A thing which is insoluble; a problem that cannot be solved.

Not soluble; in capable or difficult of being dissolved, as by a liquid.

Not to be solved or explained; insolvable.

Strong.

that cannot be dissolved