Undescribable (adjective)
alternative form of indescribable
Indescribable (adjective)
Impossible, or very difficult to describe.
“He proved it with indescribable mathematics.”
Indescribable (adjective)
Exceeding all description.
“Our hotel had an indescribable view of the Bay of Naples.”
Wiktionary
Undescribable (adjective)
too unusual, extreme, or indefinite to be adequately described; indescribable
“the very horrible, virtually undescribable quality of the urban poor”
Indescribable (adjective)
too unusual, extreme, or indefinite to be adequately described
“most prisoners suffered indescribable hardship”
Oxford Dictionary