1. In ancient Rome, a military standard or flag; or the troops serving under a separate standard; especially, a company of privileged veterans connected with a legion: The vexillum on the right is an illustration of a military banner of Roman times.
2. A banneret or a pennant: Karl was an avid collector of vexilla from many countries.
3. In Roman antiquity, a square flag, hanging transversely from the end of a spear by a wooden crosspiece, used especially by the cavalry: Again, such a vexillum is shown on the right.
4. In botany, the large upper posterior petal in a pea flower: The vexillum in a plant is also called the "banner" or the "standard".
5. In some ecclesiastical situations, a processional standard, banner, or cross: The following image is the Vatican City flag which is an example of a Catholic or church vexillum.