The Collaborative International Dictionary of English v.0.48:

Knightliness \Knight"li*ness\, n.
   The character or bearing suitable for a knight; chivalry.
   --Spenser.
   [1913 Webster]

WordNet (r) 3.0 (2006):

knightliness
    n 1: the medieval principles governing knighthood and knightly
         conduct [syn: chivalry, knightliness]