mordacious Syllabification: (mor·da·cious)Pronunciation: /môrˈdāSHəs/Definition of mordacious adjective formal 1denoting or using biting sarcasm or invective. 2(of a person or animal) given to biting. Origin: mid 17th century: from Latin mordax, mordac- 'biting' + -iousmordacious in other Oxford dictionaries Definition of mordacious in the British & World English dictionary