The Collaborative International Dictionary of English v.0.48:

digitoxin \dig`i*tox"in\ (d[i^]j`[i^]*t[o^]k"s[i^]n), n. (Chem.)
   A steroid glycoside, one of the cardiotonic chemical
   substances which is extracted from the foxglove. It is a
   white, crystalline substance (C41H64O13), and is a
   3-substituted triglucoside of a steroid, related structurally
   to digitalin and digoxin. It is used as a cardiotonic for
   treatment of certain heart conditions, such as congestive
   heart failure. Chemically it is

   (3[beta],5[beta])-3-[(O-2,6-Dideoxy-[beta]-D-ribo-hexopyranosyl-(1[rarr]4)-O-2,6-dideoxy-[beta]-D-ribo-hexopyranosyl-(1[rarr]4)-2,
   6-dideoxy-[beta]-D-ribo-hexopyranosyl)oxy]-14-hydroxy-card-20(22)-enolide.
   The related compounds digitalin and digoxin are also
   extracted from the foxglove (Digitalis lanata and
   Digitalis purpurea). The class of steroid glycosides having
   cardiotonic properties are refered to as the cardiac
   glycoside group. --MI11
   [PJC]

WordNet (r) 3.0 (2006):

digitoxin
    n 1: digitalis preparation used to treat congestive heart
         failure or cardiac arrhythmia