ETYM Cf. French réactif.
1. Tending to react to a stimulus.
2. (Chemistry and physics) Participating readily in reactions.
(Chimie) Substance dont la réaction révèle la présence d'un corps.
A substance or solution used in a chemical reaction, especially those used in laboratory work to detect, measure, or produce other substances
A chemical agent for use in chemical reactions.
Chemistry, substance used in detecting, measuring, etc. other substances by their reaction with it.