Found more than a hundred times in the New Testament, the Greek adjective “idios” meant “private” or “one’s own” as belonging to an individual.

Spicq (2:205) said whether “used as adjective, noun, or adverb, this term means ‘peculiar to, particular, private,’ but its sense is weakened in the Koine, where it is usually equivalent to a possessive.  It is used with respect to things as well as persons to express who they belong to.”

This term first occurs in Mt. 9:1 and it last used in Jude 6.  Peter used this adjective to say Scripture is not of “private” interpretation (2 Pet. 1:20).