Entry 1 sense Webster, 1913 Great-grandfather /grātˌ-grăn'-dfäthˌ-ẽr/ · Great·-grand·fa·ther · IPA /ɡrˌeɪtɡrˈændfˌɑðər/ 01 n. The father of one's grandfather or grandmother. 1. The father of one's grandfather or grandmother.