reactant reactance • reaction · · · Info · Definitions · Characters · · reactant · · Text Latin · · Script 8 · · Length Definitions · · · (noun) a chemical substance that is present at the start of a chemical reaction. · · Noun Definition 1 Characters · · a latin small letter a U+0061 c latin small letter c U+0063 e latin small letter e U+0065 n latin small letter n U+006E r latin small letter r U+0072 t latin small letter t U+0074