The C word that defines a substance that speeds a chemical reaction without being consumed is "catalyst." A catalyst is a substance that increases the rate of a chemical reaction by providing an alternative reaction pathway with a lower activation energy. It works by providing a surface for the reactant molecules to bind to, thus making it easier for them to come into contact and react. This allows the reaction to proceed more rapidly, but the catalyst itself remains unchanged at the end and can be used again in subsequent reactions. Catalysts are widely used in various industries, ranging from pharmaceuticals and petrochemicals to automobile emissions control. You can find more detailed information on the topic by visiting the Wikipedia page on catalysis at the following link: http://en.wikipedia.org/wiki/Catalysis
