Apeile is the noun form of apeilēō (G546), meaning a threat or threatening speech. It appears in Acts 4:29 and 9:1, describing the threats of the Sanhedrin against the church and Saul's threats against believers before his conversion. Also in Ephesians 6:9 where masters are warned to lay aside threatening toward slaves.
Paul's command in Ephesians 6:9 for masters to lay aside apeile (threatening) toward their servants is a radical leveling of power through the gospel. Both master and slave stand before the same heavenly Master who shows no partiality. The gospel does not merely rearrange social hierarchies — it transforms the motivations and conduct of those with power.