Grandfather
Grandpa
noun, の adjective
Your ancestor father isn't your father, it's the father that came before your father's generation, your grandfather.
The reading is all on'yomi, which is great for 祖 but not as great for 父. To remember that this 父 is ふ, just think about how much of a fool (ふ) your grandfather was, even if he wasn't.
う〜ん、何て言ったらいいのかな。僕の祖父は単なる気分屋なんだよね。機嫌がいい時もあれば、悪い時もあるっていうか。だから、あんまり気にしないで。
Hmm, how can I put this? My grandfather is just a moody guy. Sometimes he's in a good mood, sometimes he's in a bad mood. So don't worry about it too much.