Closely related to the previous term, this noun emphasizes the fixed, stable state of being firmly established. Classical sources use it of astronomical bodies' stationary positions and steady light as opposed to flickering. Rhetorically, it described sustained vocal emphasis that gave force to words—mutual support and buttressing of arguments. Peter warns believers not to fall from their 'own steadfastness,' their secure standing in truth. The term implies both present stability and the danger of displacement through deception. Translations consistently render it as 'firmness' or 'steadfastness,' recognizing the architectural metaphor of secure foundation.