The Collaborative International Dictionary of English v.0.48:

digitalin \dig"i*ta`lin\, n. [Cf. F. digitaline.]
      (a) (Medicine, Pharmacy) Any one of several extracts of
          foxglove (Digitalis), as the "French extract," the
          "German extract," etc., which differ among themselves
          in composition and properties. Both Digitalis lanata
          and Digitalis purpurea have been used to prepare
          such extracts.
      (b) (Chem.) the distinctive chemical substance, a steroid
          glycoside, which is the essential ingredient of the
          extracts of foxglove. It is a white, crystalline
          substance (C36H56O14), and is a 3-substituted
          diglucoside of a steroid. It is a powerful cardiac
          stimulant and is used as a cardiotonic for treatment
          of certain heart conditions, such as congestive heart
          failure. Chemically it is

          (3[beta],5[beta],16[beta])-3-[6-Deoxy-4-O-[beta]-D-glucopyranosyl-3-O-methyl-[beta]-D-galactopyranosyl)oxy]-14,16-dihyroxy-card-20
          (22)-enolide. The related compounds digitoxin and
          digoxin are also extracted from the foxglove. The
          class of steroid glycosides having cardiotonic
          properties are refered to as the cardiac glycosides.
          --MI11

   Syn: digitalinum verum, Diginorgin, Schmiedeberg's digitalin,
        digitalis, digitalis glycoside. [1913 Webster +PJC]

WordNet (r) 3.0 (2006):

digitalin
    n 1: a powerful cardiac stimulant obtained from foxglove [syn:
         digitalis, digitalis glycoside, digitalin]