σκληρότης G4643
sklērótēs · sklay-rot'-ace · Noun Feminine
from σκληρός; callousness, i.e. (figuratively) stubbornness:--hardness.
1 Occurrence in the King James Bible
Romans 2:5But after thy hardness and impenitent heart treasurest up unto thyself wrath against the day of wrath and revelation of the righteous judgment of God;