Easton's Bible Dictionary

(of Philippi), Acts 16:23. The conversion of the Roman jailer, a man belonging to a class "insensible as a rule and hardened by habit, and also disposed to despise the Jews, who were the bearers of the message of the gospel," is one of those cases which illustrate its universality and power.

Noah Webster's New International Dictionary of the English Language

(n.) The keeper of a jail or prison.