A.T. Robertson Commentary John 8:4

"they say unto him, Teacher, this woman hath been taken in adultery, in the very act." — John 8:4 (ASV)

Hath been taken (κατειληπτα). Perfect passive indicative of καταλαμβανω (see verse 3), caught and still guilty.

In adultery (μοιχευομενη). Present passive participle of μοιχευω, "herself suffering adultery" (Matthew 5:32). Used of married people. Not in John.

In the very act (επ' αυτοφωρω). Old adjective (αυτοφωροσ, αυτος, self, and φωρ, thief) caught in the act of theft, then extended to any crime in which one is caught. Old idiom, but not elsewhere in the Greek Bible. One example in a Berlin papyrus.