πιστός

From the study of 1 John 1:9

Range of meaning

Trustworthy, reliable, faithful (of a person who keeps faith), or believing, trusting (of a person who trusts). When it describes God, it is always the first sense: he can be relied on to keep his word.

Against the English

'Faithful' is accurate. YLT's 'stedfast' brings out the sense of reliability well. Modern readers may hear 'faithful' mainly as marital loyalty or as 'full of faith'. Here it means God keeps his promises.

Used elsewhere in the period

Deut 7:9 LXX: 'the LORD your God… is God, the faithful God (theos pistos), who keeps covenant and mercy.' Deut 32:4 LXX: 'theos pistos… dikaios kai hosios'. This is the same pairing of faithful and righteous as in our verse. Paul has 'God is faithful' (1 Cor 1:9; 10:13).

From the study of Acts 10:45

Range of meaning

Passive sense: faithful, trustworthy, reliable. Active sense: trusting or believing. In early Christian usage it became a label for members of the Jesus movement: 'the believing ones.'

Against the English

'Believers' is accurate. The word connects to pistis ('faith, trust, loyalty'), so these are people defined by their trust in and loyalty to Jesus.

Used elsewhere in the period

Acts 16:1 ('a believing Jewish woman'); 16:15; 1 Timothy 4:3, 10, 12. In ordinary Greek pistos usually means 'faithful,' as in a trustworthy servant.

From the study of 1 Corinthians 7:25

Range of meaning

Active sense: believing or trusting. Passive sense, far more common in such contexts: trustworthy, reliable, dependable, faithful to a trust.

Against the English

BSB/NIV/ESV/NASB/WEB have 'trustworthy'. KJV/YLT have 'faithful', which modern readers may hear as 'having strong faith' or 'religiously devout'.

How it drifted

In modern church English, 'faithful' has drifted toward 'loyal believer' or 'devout'. The older sense of reliable in carrying out a trust is fading.

Used elsewhere in the period

1 Cor 4:2: 'it is required of stewards that they be found pistos.' 1 Cor 1:9 and 10:13: 'God is pistos', meaning dependable. Papyri and inscriptions use it for reliable agents, slaves and officials.