The Collaborative International Dictionary of English v.0.48:

Vavasor \Vav"a*sor\, n. [OE. vavasour, OF. vavassor, vavassour,
   F. vavasseur, LL. vavassor, probably contr. from vassus
   vassorum vassal of the vassals. See Vassal.] (Feud. Law)
   The vassal or tenant of a baron; one who held under a baron,
   and who also had tenants under him; one in dignity next to a
   baron; a title of dignity next to a baron. --Burrill. "A
   worthy vavasour." --Chaucer. [Also written vavasour,
   vavassor, valvasor, etc.]
   [1913 Webster]

         Vavasours subdivide again to vassals, exchanging land
         and cattle, human or otherwise, against fealty.
                                                  --Motley.
   [1913 Webster]