Merriam-Webster Collegiate Dictionary - stoichiometry

 noun  Etymology: Greek stoicheion element (from stoichos row) + English -metry; akin to Greek steichein to walk, go — more at stair  Date: 1807  1. a branch of chemistry that deals with the application of the laws of definite proportions and of the conservation of mass and energy to chemical activity  2.  a. the quantitative relationship between constituents in a chemical substance  b. the quantitative relationship between two or more substances especially in processes involving physical or chemical change