The Collaborative International Dictionary of English v.0.48:

Guanaco \Gua*na"co\ (gw[.a]*n[aum]"k[-o]), n.; pl. Guanacos
   (-k[=o]z). [Sp. guanaco, Peruv. huanacu. Cf. Huanaco.]
   (Zool.)
   A South American mammal (Auchenia huanaco), allied to the
   llama, but of larger size and more graceful form, inhabiting
   the southern Andes and Patagonia. It is supposed by some to
   be the llama in a wild state. [Written also huanaco.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

guanaco
    n 1: wild llama [syn: guanaco, Lama guanicoe]