- any of the group of reagents produced by the interaction of magnesium and an organic halide, usually in the presence of an ether, and having the general formula RMgX, where R is an organic group and X is a halogen: used in the Grignard reaction.
- any of a class of organometallic reagents, having the general formula RMgX, where R is an organic group and X is a halogen atom: used in the synthesis of organic compounds
