The transfer of an electron to a molecular entity, resulting in a molecular entity of (algebraically) increased negative charge. It is not an attachment.
E01979.png
See also: oxidation (Def. 1), reduction
Sources:
PAC, 1991, 63, 1541. 'Recommendations for nomenclature and symbolism for mass spectroscopy (including an appendix of terms used in vacuum technology). (Recommendations 1991)' on page 1547 (https://doi.org/10.1351/pac199163101541)
PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1109 (https://doi.org/10.1351/pac199466051077)