The Collaborative International Dictionary of English v.0.48:

Adiaphorous \Ad`i*aph"o*rous\ ([a^]d`[i^]*[a^]f"[-o]*r[u^]s), a.
   [Gr. 'adia`foros; 'a priv. + dia`foros different; dia`
   through + fe`rein to bear.]
   1. Indifferent or neutral. --Jer. Taylor. AS
      [1913 Webster]

   2. (Med.) Incapable of doing either harm or good as a
      medicine. --Dunglison.
      [1913 Webster + AS]