immunotoxin Get Printable Handwriting Hear It! Say It! Write It! Learn It! Spelling Test Definition noun. a substance that can kill cells by targeting the immune system. Example Sentence The immunotoxin was used to kill cancer cells. More Example Sentences Immunotoxin can help treat certain diseases. Synonyms toxin; poison; harmful substance Antonyms healing agent; cell protector Hear It! Say It! Write It! immunotoxin Switch to cursive Start Share with your friends: