Source : Webster's Revised Unabridged Dictionary (1913)

Stoichiometry \Stoi`chi*om"e*try\, n. [Gr. ? a first principle,
   or element + -metry.]
   The art or process of calculating the atomic proportions,
   combining weights, and other numerical relations of chemical
   elements and their compounds.

Source : WordNet®

stoichiometry
     n : (chemistry) the relation between the quantities of
         substances that take part in a reaction or form a
         compound (typically a ratio of whole integers)