vector (thing)

1. An organism that spreads an infectious disease; often, this infectious host is not affected by the illness.
2. A DNA molecule that replicates on its own in a host cell and can be used as a vehicle in the laboratory for replicating other types of DNA.

From the BioTech Dictionary at http://biotech.icmb.utexas.edu/. For further information see the BioTech homenode.