in ‧ de ‧ scri ‧ ba ‧ ble /ˌɪndɪˈskraɪbəb ə l◂/ BrE AmE adjective
[ Word Family: adjective : describable ≠ ↑ indescribable , ↑ nondescript , ↑ descriptive ; verb : ↑ describe ; noun : ↑ description ; adverb : ↑ descriptively ]
something that is indescribable is so terrible, so good, so strange etc that you cannot describe it, or it is too difficult to describe:
a feeling of indescribable joy
—indescribably adverb :
an indescribably awful smell