The Collaborative International Dictionary of English v.0.48:

Jambes \Jambes\, Jambeux \Jam"beux\, n. pl. [From F. jambe a
   leg: cf. OF. jambiere. See Jamb, n.] (Ancient Armor)
   In the Middle Ages, armor for the legs below the knees,
   usually having front and back pieces; called also greaves.
   [Written also giambeux.] --Chaucer.
   [1913 Webster]