Quaternion - Vine's Expository Dictionary of New Testament Words
Quaternion[ 1,,G5069, tetradion ]
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; Matthew 28:11.