perniciousness perniciously • pernicketiness · · · Info · Definitions · Synonyms · Characters · · perniciousness · · Text Latin · · Script 14 · · Length Definitions · · · (noun) grave harmfulness or deadliness. Synonyms: toxicity. · · Noun Definition 1 Synonyms · · · toxicity · · Synonym 1 Characters · · c latin small letter c U+0063 e latin small letter e U+0065 i latin small letter i U+0069 n latin small letter n U+006E o latin small letter o U+006F p latin small letter p U+0070 r latin small letter r U+0072 s latin small letter s U+0073 u latin small letter u U+0075