1. \Qua*ter"ni*on\, n. [L. quaternio, fr. quaterni four
   each. See {Quaternary}.]
   1. The number four. [Poetic]
   2. A set of four parts, things, or person; four things taken
      collectively; a group of four words, phrases,
      circumstances, facts, or the like.
            Delivered him to four quaternions of soldiers.
                                                  --Acts xii. 4.
            Ye elements, the eldest birth Of Nature's womb, that
            in quaternion run.                    --Milton.
            The triads and quaternions with which he loaded his
            sentences.                            -- Sir W.
                                                  Scott.
   3. A word of four syllables; a quadrisyllable.
   4. (Math.) The quotient of two vectors, or of two directed
      right lines in space, considered as depending on four
      geometrical elements, and as expressible by an algebraic
      symbol of quadrinomial form.
   Note: The science or calculus of quaternions is a new
         mathematical method, in which the conception of a
         quaternion is unfolded and symbolically expressed, and
         is applied to various classes of algebraical,
         geometrical, and physical questions, so as to discover
         theorems, and to arrive at the solution of problems.
         --Sir W. R. Hamilton.
   

2. \Qua*ter"ni*on\, v. t.
   To divide into quaternions, files, or companies. --Milton.
   

a band of four soldiers. Peter was committed by Herod to the custody of four quaternions, i.e., one quaternion for each watch of the night (Acts 12:4). Thus every precaution was taken against his escape from prison. Two of each quaternion were in turn stationed at the door (12:6), and to two the apostle was chained according to Roman custom.