knight-errant

from WordNet (r) 3.0 (2006)

knight-errant
    n 1: a wandering knight travelling in search of adventure

from The Collaborative International Dictionary of English v.0.48

Knight-errant \Knight"-er`rant\, n.; pl. {Knight-errants}, or
   {Knights-errant}.
   A wandering knight; a knight who traveled in search of
   adventures, for the purpose of exhibiting military skill,
   prowess, and generosity.
   [1913 Webster]