\Pro"to-\ [Gr. prw^tos first, a superl. fr. pro` before.
See {Pro-}.]
1. A combining form prefix signifying first, primary,
   primordial; as, protomartyr, the first martyr;
   protomorphic, primitive in form; protoplast, a primordial
   organism; prototype, protozoan.
2. (Chem.)
   (a) Denoting the first or lowest of a series, or the one
       having the smallest amount of the element to the name
       of which it is prefixed; as protoxide, protochloride,
       etc.
   (b) Sometimes used as equivalent to mono-, as indicating
       that the compound has but one atom of the element to
       the name of which it is prefixed. Also used
       adjectively.