Abbott-Smith Manual Greek Lexicon
σκληρότης (G4643)
1 σκληρότης , -ητος, ἡ ( σκληρός ), [in LXX: De 9:27 ( קְשִׁי ), etc. ;] hardness ; metaph., of stubbornness: Ro 2:5 .†
G. Abbott-Smith, A Manual Greek Lexicon of the New Testament (1922) — public domain