Source : Webster's Revised Unabridged Dictionary (1913)

Hypo- \Hy"po-\ [Gr. ? under, beneath; akin to L. sub. See
   {Sub-}.]
   1. A prefix signifying a less quantity, or a low state or
      degree, of that denoted by the word with which it is
      joined, or position under or beneath.

   2. (Chem.) A prefix denoting that the element to the name of
      which it is prefixed enters with a low valence, or in a
      low state of oxidization, usually the lowest, into the
      compounds indicated; as, hyposulphurous acid.