The adjective idios, ἴδιος, which can be treated as a possessive (meaning “one’s own”), is frequent in the NT.
It is opposed to koinos, κοινός (“common”) and dēmosios, δημόσιος (“public”).
When functioning as a possessive pronoun, it has a more or less emphatic sense (e.g. Mt 9:1: ἦλθεν εἰς τὴν ἰδίαν πόλιν; “He came to His own city”).
Sometimes the word implies what is peculiar to someone (cf. 1 Cor 3:8; 7:7).
Because of the exclusive relationship that it connotes, idios, ἴδιος is not simply equivalent to the possessive genitive (e.g. “your own eye” as opposed to “your brother’s eye” in Lk 6:41).
Idios, ἴδιος is used in the relationship of the wife to her husband or vice versa (Acts 24:24; 1 Cor 7:2, 4; 14:35; Eph 5:22; Col 3:18 ; Tit 2:5; 1 Pet 3:1, 5) and with reference to the family or the household (cf. 1 Tim 3:4, 5, 12; 5:4).
In a similar vein, it applies to the relationship between God the Father and His Son Jesus Christ (Jn 5:18; Rom 8:32).
The word may apply to private property (Acts 4:32), an individual’s circumstance or condition (e.g., Mt 25:15; Jn 7:18; Rom 10:3; 1Cor 3:8), and God’s appointed time (Gal 6:9; 1 Tim 2:6; 6:15; Tit 1:3).
As an adverb
When used as an adverb, idios, ἴδιος means “by oneself” or “privately.”
Thus, the Spirit distributes “by Himself” to each just as He wills (1 Cor 12:11).
κατ’ ἰδίαν appears numerous times, particularly in the Gospels, such as when it is said that Jesus withdrew by Himself or took the disciples aside privately (Mt 14:13, 23; 17:1, 19; 20:17; 24:3; Mk 4:34; 6:31f.; 7:33; 9:2, 28; 13:3; Lk 9:10; 10:23).
Substantive use
The substantive οἱ ἴδιοι in certain non-biblical literature has the meaning of comrades in battle or compatriots.
Hence we may understand Acts 4:23 and 24:23 as references to fellow Christians.
οἱ ἴδιοι is also used of one’s relatives, and hence 1 Tim 5:8 speaks of providing for one’s household.
As it does in Greek literature, τὰ ἴδια in Jn 16:32, 19:27, and Acts 21:6 means “home.” But in certain instances it may carry the broader meaning of one’s possessions (Lk 18:28; Jn 8:44).
