Lewis & Short

vexillātĭo, ōnis, f. [vexillum].

  1. I. A body of the vexillarii; acc. to others, a body of soldiers united under one flag (vexillum), a corps, battalion, Suet. Galb. 20; Inscr. Orell. 845; 2009 sq. al.
  2. II. A division of cavalry, a troop, squadron, Veg. Mil. 2, 1; Amm. 25, 1, 9; App. M. 7, p. 191, 3.