1A noun meaning grandfather — the father of one's parent; commonly used in family contexts.
私の祖父は戦争の話をよくしてくれた。
My grandfather often told me stories about the war.
毎週日曜日は祖父の家に行く。
I go to my grandfather's house every Sunday.
祖父の写真をアルバムに入れた。
I put my grandfather's pictures into the album.
2An old-fashioned meaning of 'old man' or 'elderly man', used only with the archaic reading おおじ; rarely encountered in modern speech.
3In traditional performing arts such as kyogen, refers to the mask used for an old man's role; a specialized term read only as おおじ.
能楽の公演では祖父（おおじ）の面が使われた。
In the Noh performance, an 'ooji' old-man mask was used.