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

acid acidity agent alkali alkalinity alloisomer anion antacid atom base biochemical cation chemical chemical element chromoisomer compound copolymer dimer element heavy chemicals high polymer homopolymer hydracid inorganic chemical ion isomer macromolecule metamer molecule monomer neutralizer nonacid organic chemical oxyacid polymer pseudoisomer radical sulfacid trimer