cytotoxic adjective 2noun 1forms 3 adjective2 •Of, relating to, or being a cytotoxin. •Of or relating to cytotoxicity. noun1 •Any cytotoxic substance; a cytotoxin.Current chemotherapies for cancer are mostly cytotoxics with serious side effects and high incidence of drug resistance. — 2015 formscytotoxics · more cytotoxic · most cytotoxic