That which cannot be explained - inexplicable (अकथनीय)
That which can not be hurt - invulnerable (अभेद्य)
That which can not be imitated - inimitable (अनोखा)
That which can not be noticed - imperceptible (अगोचर/ अतिसूक्ष्म)
That which can not be practiced - impracticable (अव्यावहारिक)
That which can not be satisfied - insatiable (लालची)
That which does not bear the name of the writer - anonymous (नामरहित)
That which is against law - illegal (अवैध)
That which is lawful - legal (कानूनी)
That which is unlikely to happen - improbable (असंभव)