The Collaborative International Dictionary of English v.0.48:

Argo \Ar"go\, n. [L. Argo, Gr. ?.]
   1. (Myth.) The name of the ship which carried Jason and his
      fifty-four companions to Colchis, in quest of the Golden
      Fleece.
      [1913 Webster]

   2. (Astron.) A large constellation in the southern
      hemisphere, called also Argo Navis. In modern astronomy
      it is replaced by its three divisions, Carina, Puppis, and
      Vela.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Argo
    n 1: formerly a large constellation in the southern hemisphere
         between Canis Major and the Southern Cross; now divided
         into Carina and Pyxis and Puppis and Vela