The Collaborative International Dictionary of English v.0.48:

Carcanet \Car"ca*net\ (k[aum]r"k[.a]*n[e^]t), n. [Dim. fr. F.
   carcan the iron collar or chain of a criminal, a chain of
   precious stones, LL. carcannum, fr. Armor. kerchen bosom,
   neck, kelchen collar, fr. kelch circle; or Icel. kverk troat,
   OHG. querca throat.]
   A jeweled chain, necklace, or collar. [Also written
   carkanet and carcant.] --Shak.
   [1913 Webster]