ineffable

/ɪnˈɛf.ə.bəl/

adjective

  1. Too great, exquisite, or sacred to be expressed or described in words. "Standing at the edge of the Grand Canyon at sunrise inspired an ineffable sense of awe."
  2. Not to be uttered; taboo because of religious or sacred sanctity. "In several ancient esoteric traditions, the true name of the creator is considered ineffable."