reagent

A substance used in a chemical reaction to detect, measure, examine, or produce other substances.

In experimental psychology: The observer in any form of psychological experiment: opposed to experimenter.

Same as reactor.

One who or that which exerts reflex action or influence; an agency that produces reciprocal effects; a cause or source of counter-results.

In chem., a substance used to effect chemical change in another substance for the purpose of identifying its component parts or of ascertaining its percentage composition.

Anything used for the treatment of a substance under investigation to render its nature or condition more evident.

A substance capable of producing with another a reaction, especially when employed to detect the presence of other bodies; a test.

A usually available or readily made compound or known mixture of compounds used to treat materials, samples, other compounds or reactants in a laboratory or sometimes an industrial setting.

a chemical agent for use in chemical reactions