Strong’s Greek
G4104 — pistoo
The entry below is Strong’s own definition (1890, public domain), and every verse where the word occurs.
πιστόομαι
pistoo — pronounced pis-to'-o
from 4103; to assure:--assure of. see GREEK for 4103
1 occurrence in the KJV.
2 Timothy 3:14
But continue thou in the things which thou hast learned and hast been assured of, knowing of whom thou hast learned them;