[1] : The Collaborative International Dictionary of English v.0.48

proto- \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.
      1913 webster

   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.
          1913 webster
see also:
pro- 

[2] : WordNet (r) 2.0

proto
     adj : indicating the first or earliest or original; "`proto' is a
           combining form in a word like `protolanguage' that
           refers to the hypothetical ancestor of another language
           or group of languages" syn: protoa
see also:
protoa 

Proto- >> P Words
Proto-, definition of term: Proto-
proto-_pag1.html