Mainspring and Reactant

Mainspring noun - The most important spring in a mechanical device (especially a clock or watch); as it uncoils it drives the mechanism.

Reactant and mainspring are semantically related. In some cases you can use "Reactant" instead a noun "Mainspring".

Reactant noun - A chemical substance that is present at the start of a chemical reaction.

Mainspring and reactant are semantically related. Sometimes you can use "Mainspring" instead a noun "Reactant".