noun
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.
亡祖父は生前、教師をしておりました。
My late grandfather was a teacher during his lifetime.
この家は亡祖父が建てたものです。
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.