"外祖父" 用英语称为 "paternal grandfather"，"爷爷" 用英语称为 "grandfather"，"外公" 用英语称为 "maternal grandfather"，"姥爷" 用英语称为 "grandfather (informal term)"。
"Paternal" 来自拉丁语 "pater"，意为父亲；"maternal" 来自拉丁语 "mater"，意为母亲。
例句:
My paternal grandfather was a farmer.
(我的外祖父是个农民)
My grandfather always tells me stories about his childhood.
(我爷爷总是给我讲他童年时的故事)
My maternal grandfather was a teacher.
(我的外公是个老师)
My grandfather passed away last year.
(我的姥爷去年去世了)