Ineffable
Definition:
(adj)
1. Beyond description; indescribable
2. Not to be uttered; taboo
Synonyms:
Unspeakable, indescribable
Antonyms:
Describable
Sentences:
Bob was so good at basketball that Sally said that is skills were ineffable.
In the Harry Potter series, no one is allowed to say Voldemort's name, making it ineffable.
Milford Sound, NZ, Waterfalls, Fiordland National Park.