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

vassalage \vas"salage\, n. oe. vassalage, f. vasselage, ll.
   vassallaticum.
   1913 webster
   1. the state of being a vassal, or feudatory.
      1913 webster

   2. political servitude; dependence; subjection; slavery; as,
      the greeks were held in vassalage by the turks.
      1913 webster

   3. a territory held in vassalage. "the countship of foix,
      with six territorial vassalages." --milman.
      1913 webster

   4. vassals, collectively; vassalry. r. --shak.
      1913 webster

   5. valorous service, such as that performed by a vassal;
      valor; prowess; courage. obs. --chaucer.
      1913 webster

[2] : WordNet (r) 2.0

vassalage
     n : the state of a serf syn: serfdom, serfhood
see also:
serfdom serfhood 

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

30 moby thesaurus words for "vassalage":
   absolutism, bond service, bondage, captivity, control,
   debt slavery, deprivation of freedom, disenfranchisement,
   disfranchisement, domination, enslavement, enthrallment, feudalism,
   feudality, helotism, helotry, indentureship, peonage, restraint,
   serfdom, serfhood, servility, servitude, slavery, subjection,
   subjugation, thrall, thralldom, tyranny, villenage

Vassalage >> V Words
Vassalage, definition of term: Vassalage
vassalage_pag1.html