https://doi.org/10.1351/goldbook.E01988
  1. A
    molecular entity
    that can transfer an electron to another molecular entity, or to the corresponding chemical species.
  2. [obsolete] A
    Lewis base
    . This use is discouraged.
Source:
PAC, 1994, 66, 1077. (Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)) on page 1110 [Terms] [Paper]