supernova Syllabification: (su·per·no·va)Pronunciation: /ˈso͞opərˌnōvə/Definition of supernova noun (plural supernovae /-ˌnōvē/ or supernovas) Astronomy a star that suddenly increases greatly in brightness because of a catastrophic explosion that ejects most of its mass. supernova in other Oxford dictionaries Definition of supernova in the British & World English dictionary