A substance to which an electron may be transferred; for example 1,4-dinitrobenzene or the dication 1,1'-dimethyl-4,4'-bipyridyldiium.
Source: PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1109 (https://doi.org/10.1351/pac199466051077)
[obsolete] A Lewis acid. This usage is discouraged.