Peitho (G3982) is the persuasion family β active voice: to convince someone; passive voice: to be persuaded, to trust, to have confidence. The perfect passive pepoitha β 'I am fully persuaded' β is Paul's signature confidence word: 'I am convinced [pepoitha] that neither death nor life... will be able to separate us from the love of God' (Romans 8:38).
Philippians 1:6 declares: 'I am confident [pepoihos] of this, that he who began a good work in you will carry it on to completion.' This is not self-confidence but God-confidence β trust rooted in the character and promises of God. The word also appears for human persuasion (Acts 13:43; 18:4) and for the danger of trusting in the wrong things (Philippians 3:4 β 'confidence in the flesh').