Immunotoxin can be defined as a poisonous substance that is capable of killing cells or tissues that are not immune to it. However, there are several synonyms that can be used interchangeably with this term. One of them is cytotoxin, which is a substance that can kill or damage cells. Another synonym is a toxin, which is a harmful substance produced by living organisms, including bacteria, fungi, and plants. Moreover, there is the term biologic therapy, which refers to the use of biological agents to treat diseases. Lastly, there is the word biotherapeutic, which refers to any substance that is used to treat diseases by targeting specific cells or tissues while leaving healthy ones unharmed.