<p><strong>Adjective</strong></p><ul><li>of, pertaining to, affected with, or caused by a toxin or poison: a toxic condition.</li><li>acting as or having the effect of a poison; poisonous: a toxic drug.</li><li>causing unpleasant feelings; harmful or malicious: toxic criticism.</li><li>a toxic boyfriend who wanted complete control over her; toxic criticism.</li><li>Finance. pertaining to or noting debt that will probably not be repaid: toxic mortgages.</li><li>pertaining to or noting a financial instrument or other asset that has no value or an unknown value because there is no market for it: toxic mortgage-backed securities.</li></ul><p><strong>Noun</strong></p><ul><li>a toxic chemical or other substance.</li></ul>