Strong’s Greek
G215 — alaletos
The entry below is Strong’s own definition (1890, public domain), and every verse where the word occurs.
ἀλάλητος
alaletos — pronounced al-al'-ay-tos
from 1 (as a negative particle) and a derivative of 2980; unspeakable:--unutterable, which cannot be uttered. see GREEK for 1 see GREEK for 2980
1 occurrence in the KJV.
Romans 8:26
Likewise the Spirit also helpeth our infirmities: for we know not what we should pray for as we ought: but the Spirit itself maketh intercession for us with groanings which cannot be uttered.