indescribably vs inexpressibly

indescribably and inexpressibly both are adverbs.

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

As adverbs, indescribably and inexpressibly are synonyms defined as:

Other synonyms of indescribably include ineffably, unspeakably, unutterably.

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