E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
A youth. In feudal times it meant a feudatory, or one who held lands under a lord. In law it means a bondservant or political slave, as England shall never be the vassal of a foreign prince. Christian says, in his Notes on Blackstone, that the corruption of the meaning of vassal into slave is an incontrovertible proof of the horror of feudalism in England. (Welsh, gwas, a boy or servant; gwasan, a page; like the French garçon, and Latin puer; Italian, vassallo, a servant.)