The Greek verb koinoō (from koinos, common) means to make common or to defile — in ritual contexts, to bring something into the realm of the profane or unclean. It is the opposite of hagiazō (to sanctify/make holy). It appears in Matthew 15:11 (what enters the mouth does not defile — koinoi — a man), Acts 10:15 (what God has made clean do not koinou), and Hebrews 9:13 (the blood of animals sanctifying those who are kekoinōmenous).
Jesus' teaching on koinoō in Matthew 15:11–20 radically reframes defilement: it is not what goes into the mouth that defiles but what comes out of the heart. This is not the abolition of holiness but its internalization — the source of true contamination is not dietary but moral. Acts 10:15 brings this to its missional conclusion: what God has cleansed — the Gentiles — is not to be called koinon (common/defiled). The gospel dismantles the ritual wall between clean and unclean peoples, making the uncircumcised holy through the blood of Christ.