carrier atom

in organic reaction mechanisms
https://doi.org/10.1351/goldbook.C00861
A participant atom which is neither core nor peripheral and which carries other groups to and from the molecule containing the @[email protected] but which does not itself become covalently attached to that molecule.
Source:
PAC, 1989, 61, 23. (System for symbolic representation of reaction mechanisms (Recommendations 1988)) on page 27 [Terms] [Paper]