of an army is the French avant, but van, a winnowing machine, is the Latin vannus, our fan.
The Spirit of the Van. A sort of fairy which haunts the Van Pools in the mountains of Carmarthen on New Year's Eve. She is dressed in white, girded with a golden girdle; her golden hair is very long, and she sits in a golden boat, which she urges along with a golden oar. A young farmer fell in love with her and married her, but she told him if he struck her thrice she would quit him for ever. After a time they were invited to a christening, and in the midst of the ceremony she burst into tears. Her husband struck her, and asked why she made such a fool of herself. “I weep,” she said, “to see the poor babe brought into a vale of misery and tears.” They were next invited to the funeral of the same child, and she could not resist laughing. Her husband struck her again, and asked the same question. “I laugh,” she said, “to think how joyous a thing it is that the child has left a world of sin for a world of joy and innocence.” They were next invited to a wedding, where the bride was young and the man advanced in years. Again she wept, and said aloud. “It is the devil's compact. The bride has sold herself for gold.” Her husband bade her hold her peace, struck her, and she vanished for ever from his sight. (Welsh mythology.)
(pl. Vanir), in Scandinavian mythology. Gods of the ocean, air, fountains, and streams.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894