That which cannot be divided or split.
An infinitely small quantity which is assumed to admit of no further division.
Incapable of being divided; atomic.
Incapable of being divided by a specific integer without leaving a remainder.
Any substance that cannot be dissolved.
That cannot be dissolved.
That cannot be solved; unsolvable; insolvable.
That cannot be explained; mysterious or inexplicable.
That cannot be broken down or dispersed.