in ‧ ex ‧ pres ‧ si ‧ ble /ˌɪnɪkˈspresəb ə l◂, ˌɪnɪkˈspresɪb ə l◂/ BrE AmE adjective formal
[ Word Family: adverb : ↑ expressively , ↑ expressionlessly , ↑ inexpressibly ; adjective : ↑ expressive ≠ ↑ inexpressive , ↑ expressionless , ↑ inexpressible ; noun : ↑ expression , ↑ expressiveness ; verb : ↑ express ]
an inexpressible feeling is too strong to be described in words:
inexpressible gratitude
—inexpressibly adverb