The Greek noun suneidesis (συνείδησις) means conscience — the inner moral faculty by which one is aware of right and wrong, and experiences guilt or approval accordingly. It appears about 32 times in the NT. It literally means 'co-knowledge' — knowing with oneself.
Suneidesis is the NT's primary word for moral self-awareness. Paul declares his conscience (suneidesis) clear (Acts 23:1; 24:16) as he stands before tribunals. The conscience bears witness to God's law written on human hearts — even Gentiles have a conscience that accuses or defends them (Romans 2:15). A key pastoral concern: a 'weak' conscience can be damaged by others' actions (1 Corinthians 8:10–12), and believers must not act against their conscience (Romans 14:23). The goal is a 'good conscience' (kale suneidesis, 1 Timothy 1:5, 19; Hebrews 13:18; 1 Peter 3:16). Hebrews 9:14 declares that the blood of Christ 'cleanses our conscience (suneidesin) from acts that lead to death, so that we may serve the living God' — the deepest cleansing goes to the level of moral self-awareness.