active, active agent - chemical agent capable of activity

agent - a substance that exerts some force or effect

reagent - a chemical agent for use in chemical reactions

desiccant, drier, drying agent, sicative - a substance that promotes drying (e.g., calcium oxide absorbs water and is used to remove moisture)

oxidant, oxidiser, oxidizer, oxidizing agent - a substance that oxidizes another substance

reducer, reducing agent, reductant - a substance capable of bringing about the reduction of another substance as it itself is oxidized; used in photography to lessen the density of a negative or print by oxidizing some of the slackened silver

scavenger - a chemical agent that is added to a chemical mixture to counteract the effects of impurities

surface-active agent, surfactant, wetter, wetting agent - a substance capable of reducing the surface tension of a liquid in which it is dissolved

vesicant, vesicatory - a chemical agent that causes blistering