1. 言语难以表达的;不可言喻的
You use ineffable to say that something is so great or extreme that it cannot be described in words.

1. defying expression or description

e.g. indefinable yearnings
indescribable beauty
ineffable ecstasy
inexpressible anguish
unspeakable happiness
unutterable contempt
a thing of untellable splendor

Synonym: indefinableindescribableunspeakableuntellableunutterable

2. too sacred to be uttered

e.g. the ineffable name of the Deity

Synonym: unnameableunspeakableunutterable