tombstone Syllabification: (tomb·stone)Pronunciation: /ˈto͞omˌstōn/Translate tombstone | into French | into German | into Italian | into Spanish Definition of tombstone noun 1a large, flat inscribed stone standing or laid over a grave. 2 (also tombstone advertisement or tombstone ad) an advertisement listing the underwriters or firms associated with a new issue of securities. tombstone in other Oxford dictionaries Definition of tombstone in the British & World English dictionary