Smith's Bible Dictionary
Quaternion. A military term, signifying a guard of four soldiers, two of whom were attached to the person of a prisoner, while the other two kept watch, outside the door of his cell. Acts 12:4.
These files are public domain.
Smith, William, Dr. Entry for 'Quaternion'. Smith's Bible Dictionary. https://www.studylight.org/dictionaries/eng/sbd/q/quaternion.html. 1901.