Strong's G4644 — σκληροτράχηλος (adjective)
sklerotrachelos (sklay-rot-rakh'-ay-los) adj.
1. hardnaped
2. (figuratively) obstinate
[from G4642 and G5137]
KJV: stiffnecked 
Root(s): G4642, G5137 
Hebrew root: τράχηλος
Occurrences: 1