οἰκεῖοςoikeîos

in or of the house (opposed to ξένος, ἀλλότριος)

Greek (New Testament) · G3609

Meanings

(a) of things; τὰ οἰ., household affairs or goods

(b) of persons, of the same family or kin; as as a noun, οἱ οἰ., kinsmen: 1 Timothy 5:8; with genitive of person, of the family of: metaphorically, τ. θεοῦ, Ephesians 2:19; τ. πίστεως, Galatians 6:10.

Synonyms

συγγενής, ἴδιος.

Same root

οἶκοςoîkos · G3624a dwelling (more or less extensive, literal or figurative); by implication, a family (more or less related, literally or figuratively)

Where it appears

Appears 3 times in the Bible.

Galatians 6:10 Therefore, whenever we have the opportunity, we should do good to everyone—especially to those in the family of faith.
Ephesians 2:19 So now you Gentiles are no longer strangers and foreigners. You are citizens along with all of God’s holy people. You are members of God’s family.
1 Timothy 5:8 But those who won’t care for their relatives, especially those in their own household, have denied the true faith. Such people are worse than unbelievers.

Source: G. Abbott-Smith, A Manual Greek Lexicon of the New Testament (1922), public domain.