A.T. Robertson Commentary Acts 5:18

"and laid hands on the apostles, and put them in public ward." — Acts 5:18 (ASV)

With jealousy (ζηλου). Genitive case. Old word from zeo, to boil, our zeal. In itself it means only warmth, ardour, zeal, but for a bad cause or from a bad motive, jealousy, envy, rivalry results (Acts 13:45). Common in the epistles.

In public ward (εν τηρησε δημοσια). As in 4:3 only with δημοσια (public) added, in the public prison, perhaps not the "common" prison, but any prison is bad enough. In verse 19 it is called "the prison" (της φυλακης), the guardhouse.