Entry 1 sense Webster, 1913 Great-grandmother /grātˌ-grăn'-dmŭthˌ-ẽr/ · Great·-grand·moth·er · IPA /ɡrˌeɪtɡrˈændmˌʌθər/ 01 n. The mother of one's grandfather or grandmother. 1. The mother of one's grandfather or grandmother.