This word is acceptable for play in the US & UK dictionaries that are being used in the following games:

• Lexulous
• Wordscraper
• Wordosaur

adj. Not readily spoken or expressed: unsayable fears.

n. Something not readily said.

n. Something unfit to be said.

adj. Not capable of being said.

adj. Not allowed or not fit to be said.

"Although much of the early history of the restaurant is "unsayable" - according to Sir George, that's only partly due to the romantic liaisons which started there."

unsayably   

unutterable    inexpressible    ineffable    unspeakable    taboo   

unshed    squawky    unthought    eeriest    half-painful