That cannot be described; beyond the power of description
The definition of incredible is something so unbelievable or so unusual that it is hard to believe.
That cannot be defined
Not to be uttered; taboo:
The definition of remarkable is something unusual, extraordinary or worthy of attention.
Not fit to be mentioned.
Not to be named or identified:
Find another word for unutterable. In this page you can discover 20 synonyms, antonyms, idiomatic expressions, and related words for unutterable, like: indescribable, incredible, unspeakable, incommunicable, indefinable, ineffable, inexpressible, undescribable, defying description, words and remarkable.