Source : Webster's Revised Unabridged Dictionary (1913)

Serpentarius \Ser`pen*ta"ri*us\, n.[NL., fr. L. serpens
   serpent.] (Astron.)
   A constellation on the equator, lying between Scorpio and
   Hercules; -- called also {Ophiuchus}.

Ophiuchus \O`phi*u"chus\, n. [L., fr. Gr. ?, lit., holding a
   serpent; 'o`fis a serpent + ? to hold.] (Astron.)
   A constellation in the Northern Hemisphere, delineated as a
   man holding a serpent in his hands; -- called also
   {Serpentarius}.

Source : WordNet®

Ophiuchus
     n : a large constellation in the equatorial region between
         Hercules and Scorpius