π-electron donor 

https://doi.org/10.1351/goldbook.08201
Substituent capable of electron donation by resonance (e.g., \(\ce{OCH3}\)).
Source:
PAC, 2022, 94, 353. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 2021)' on page 491 (https://doi.org/10.1515/pac-2018-1010)