Originally describing physical putrefaction — rotten fruit, stale fish, decayed wood — sapros takes on a moral and qualitative sense in Jesus's teaching. In the tree-and-fruit metaphor (Matt 7:17-18; 12:33), a 'bad' tree cannot produce good fruit. In the parable of the dragnet (Matt 13:48), 'rotten' fish are sorted out and thrown away. Ephesians 4:29 applies the term to speech: no 'rotten' word should come from your mouth. The physical-to-moral trajectory is strikingly consistent. French 'pourri' and German 'faul' both preserve the concrete decay imagery that underlies the metaphorical extension.