indescribably vs ineffably

indescribably and ineffably both are adverbs.

Word	Noun	Adjective	Verb	Adverb
indescribably	No	No	No	Yes
ineffably	No	No	No	Yes

As adverbs, indescribably and ineffably are synonyms defined as:

Other synonyms of indescribably include inexpressibly, unspeakably, unutterably.

indescribably (adverb)	ineffably (adverb)
to an inexpressible degree	to an inexpressible degree