► 名詞御祖父さん [(2)おじいさん]
meaning: grandfather rank: 1☆ うちの御祖父さん ⇨ My grandfather
お祖父ちゃん [(2)おじいちゃん] [coll] [family]
meaning: grandfather rank: 1☆ おじいちゃん！ ⇨ Grandpa!
(☛ Most informal)祖父 [(1)そふ] [liter]
meaning: grandfather rank: 2☆
私の祖父 ⇨ My grandfather
(☛ Most formal)