Pronunciation: (fāt'l),[key] —adj. 1. causing or capable of causing death; mortal; deadly: a fatal accident; a fatal dose of poison. 2. causing destruction, misfortune, ruin, or failure: The withdrawal of funds was fatal to the project. 3. decisively important; fateful: The fatal day finally arrived. 4. proceeding from or decreed by fate; inevitable: a fatal series of events. 5. influencing or concerned with fate; fatalistic.