Merriam-Webster Collegiate Dictionary - antitoxin

 noun  Etymology: International Scientific Vocabulary  Date: circa 1890 an antibody that is capable of neutralizing the specific toxin (as a specific causative agent of disease) that stimulated its production in the body and is produced in animals for medical purposes by injection of a toxin or toxoid with the resulting serum being used to counteract the toxin in other individuals; also an antiserum containing ~s