The Collaborative International Dictionary of English v.0.48:

Hydr- \Hy"dr-\
   See under Hydro-.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Hydro- \Hy"dro-\, Hydr- \Hy"dr-\
   1. A combining form from Gr. ?, ?, water (see Hydra).
      [1913 Webster]

   2. (Chem.) A combining form of hydrogen, indicating hydrogen
      as an ingredient, as hydrochloric; or a reduction product
      obtained by hydrogen, as hydroquinone.
      [1913 Webster]