"a group of four" (tetra---, "four"), occurs in Acts 12:4 . A "quaternion" was a set of four men occupied in the work of a guard, two soldiers being chained to the prisoner and two keeping watch; alternatively one of the four watched while the other three slept. The night was divided into four watches of three hours each; there would be one "quaternion" for each watch by day and by night. Cp. the "guard" in Matthew 27:65; 28:11 .
With over 3,400 entries, this timeless classic is THE reference guide to New Testament Greek words for English readers. It explains the meaning of the original Greek with the added dimension of the context of the Greek word.Wikipedia
Read More