This noun has two distinct but related meanings: rust or corrosion on metal, and poison or venom from serpents. Romans 3:13 quotes Psalm 140, 'the poison of asps is under their lips,' describing human speech as venomous. James 3:8 calls the tongue 'full of deadly poison,' extending the venom metaphor. James 5:3 speaks literally of rust: 'your gold and silver have rusted, and their rust will be a witness against you.' Classical usage includes rust on iron, verdigris on copper, and patina on bronze. The word's dual sense—corrosion that destroys metals and venom that kills—makes it apt for describing anything with destructive, corrupting power.