1 a person or thing that carries, holds, or conveys something: water carriers.
2 a person or company that undertakes the professional conveyance of goods or people: Pan Am was the third US carrier to cease operations in 1991.
• a vessel or vehicle for transporting people or things, esp. goods in bulk: the largest timber carrier ever to dock at a Malaysian port.
• an aircraft carrier.
• a company that provides facilities for conveying telecommunications messages.
3 a person or animal that transmits a disease-causing organism to others. Typically, the carrier suffers no symptoms of the disease: the black rat, best known as carrier of bubonic plague.
• a person or other organism that possesses a particular gene, esp. as a single copy whose effect is masked by a dominant allele, so that the associated characteristic (such as a hereditary disease) is not displayed but may be passed to offspring.
4 a substance used to support or convey another substance such as a pigment, catalyst, or radioactive material.
• Physics short for charge carrier.
• Biochemistry a molecule that transfers a specified molecule or ion within the body, esp. across a cell membrane.