[1] : 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
see also:
valet varlet vavasor rear vassal 

[2] : The Collaborative International Dictionary of English v.0.48

vassal \vas"sal\, a.
   resembling a vassal; slavish; servile.
   1913 webster

         the sun and every vassal star.           --keble.
   1913 webster

[3] : The Collaborative International Dictionary of English v.0.48

vassal \vas"sal\, v. t.
   to treat as a vassal; to subject to control; to enslave.
   obs. --beau.  fl.
   1913 webster

[4] : WordNet (r) 2.0

vassal
     n : a person holding a fief syn: liege, liegeman, liege
         subject, feudatory
see also:
liege liegeman liege subject feudatory 

[5] : Moby Thesaurus II by Grady Ward, 1.0

47 moby thesaurus words for "vassal":
   bondmaid, bondman, bondslave, bondsman, bondswoman, captive,
   chattel, chattel slave, churl, client, concubine, creature,
   debt slave, dependent, feudal, feudatory, flunky, follower,
   galley slave, hanger-on, helot, homager, inferior, lackey, liege,
   liege man, liege subject, minion, myrmidon, odalisque, peon,
   retainer, serf, servant, servile, slave, stooge, subject,
   subordinate, subservient, theow, thrall, tributary, underling,
   understrapper, villein, yeoman

[6] : Bouvier's Law Dictionary, Revised 6th Ed (1856)

vassal, feudal law. this was the name given to the holder of a fief, bound 
to perform feudal service; this word was then always correlative to that of 
lord, entitled to such service. 
     2. the vassal himself might be lord of some other vassal. 
     3. in aftertimes, this word was used to signify a species of slave who 
owed servitude, and was in a state of dependency on a superior lord. 2 bl. 
com. 53; merl. repert. h.t. 

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