1. An antibiotic that carries specific ions across a membrane; such as, the plasma membrane of bacterial or animal cells or the mitochondrial membrane.
2. Any molecule; such as, of a drug, that increases the permeability of cell membranes to a specific ion.
3. Any of a group of organic compounds that facilitate the transport of ions across a cell membrane.
4. A chemical compound capable of forming a complex with an ion and transporting it through a biological membrane.
5. A lipid-soluble substance capable of transporting specific ions through cellular membranes.
6. A chemical material that has a high affinity for ions.

Ionophores are used in ion-selective electrode membranes.