quaternion

Boyd’s Bible Dictionary:

(file of four). A Roman guard of four soldiers two of whom watched prisoners within the door, and two watched the door outside ({vi 27342-27348}Acts 12:4-10).

Concise Bible Dictionary:

A party of “four soldiers.” Four such parties were told off to guard Peter when in prison, that they might relieve each other every three hours in the night (Acts 12:4).

Strong’s Dictionary of Greek Words:

Number:
5069 (find all occurrences in KJV Bible)
Greek:
τετράδιον
Transliteration:
tetradion
Phonic:
tet-rad’-ee-on
Meaning:
neuter of a presumed derivative of τέτρας (a tetrad; from 5064); a quaternion or squad (picket) of four Roman soldiers
KJV Usage:
quaternion