electron donor

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 (https://doi.org/10.1351/pac199466051077)