Latin word vexillum comes from Proto-Indo-European *weg, and later Latin velum (A cloth, curtain, veil, awning. The sail of a ship.)

Detailed word origin of vexillum

Dictionary entry	Language	Definition
*weg	Proto-Indo-European (ine-pro)
velum	Latin (lat)	A cloth, curtain, veil, awning. The sail of a ship.
vexillum	Latin (lat)	Flag, banner.