deceased grandfather; late grandfather
Formal or respectful term for one's own grandfather who has passed away. Used in written contexts, obituaries, or when speaking politely about family history.
My late grandfather was a teacher during his lifetime.
This house was built by my deceased grandfather.
故祖父 also means 'deceased grandfather', but 亡祖父 is more common in modern usage.
Compound of 亡 (ぼう, 'deceased') + 祖父 (そふ, 'grandfather'). The reading ぼうそふ follows standard on'yomi readings for both characters.