The Collaborative International Dictionary of English v.0.48:

Indo-Germanic \In`do-Ger*man"ic\, a. [Indo- + Germanic.]
   [1913 Webster]
   1. Same as Aryan, and Indo-European.
      [1913 Webster]

   2. Pertaining to or denoting the Teutonic family of languages
      as related to the Sanskrit, or derived from the ancient
      Aryan language.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Indo-Germanic
    adj 1: of or relating to the Indo-European language family [syn:
           Indo-European, Indo-Germanic]