car·ri·er (kărˈē-ər)

1. A person or an animal that shows no symptoms of a disease but harbors the infectious agent of that disease and is capable of transmitting it to others.
2. A compound capable of transferring a hydrogen atom from one compound to another.
3. A quantity of naturally occurring element added to a minute amount of pure isotope, especially a radioactive one, to facilitate the chemical handling of the isotope.
4. An individual that carries, but does not express, a gene for a particular recessive trait, yet when mated with another carrier, can produce offspring that do.