The Collaborative International Dictionary of English v.0.48:

Vassal \Vas"sal\, n. [F., fr. LL. vassallus, vassus; of Celtic
   origin; cf. W. & Corn. gwas a youth, page, servant, Arm. gwaz
   a man, a male. Cf. Valet, Varlet, Vavasor.]
   [1913 Webster]
   1. (Feud. Law) The grantee of a fief, feud, or fee; one who
      holds land of a superior, and who vows fidelity and homage
      to him; a feudatory; a feudal tenant. --Burrill.
      [1913 Webster]

   2. A subject; a dependent; a servant; a bondman; a slave.
      "The vassals of his anger." --Milton.
      [1913 Webster]

   Rear vassal, the vassal of a vassal; an arriere vassal.
      [1913 Webster]