Strong’s Greek
G4644 — sklerotrachelos
The entry below is Strong’s own definition (1890, public domain), and every verse where the word occurs.
σκληροτράχηλος
sklerotrachelos — pronounced sklay-rot-rakh'-ay-los
from 4642 and 5137; hardnaped, i.e. (figuratively) obstinate:--stiffnecked. see GREEK for 4642 see GREEK for 5137
1 occurrence in the KJV.
Acts 7:51
Ye stiffnecked and uncircumcised in heart and ears, ye do always resist the Holy Ghost: as your fathers did, so do ye.