同姓どうせい (dousei)

日本にっぽんでは夫婦ふうふ同姓どうせいが一般いっぱん的てきよ。

In Japan, it's common for a married couple to have the same surname.

異音同姓に一色田がある。

There is Isshikida as the same surname but with a different pronunciation.

異音同姓（わたりだ）渡田がある。

There is Watada, pronounced Watarida, as the same surname with a different pronunciation.

彼らは同姓だが何のつながりもない.

They have the same family name but are not in any way related to each other.

私わたしは私わたしと同姓どうせい同名どうめいの女おんなの人ひとをしっている。

I know a woman whose first and last names are the same as mine.

大坂の陣では同姓の誼で毛利勝永の部隊にいたとある。

It is recorded that he was in the army of Katsunaga MORI at Osaka no Jin (The Siege of Osaka) for the sake of having the same family name.

渡田.異音同姓（わたのべ）に渡野辺、渡延、渡野邊がある。

As surnames pronounced Watanobe with different characters, there are Watanobe, Watanobu, and Watanobe.

渡野辺,渡延or渡野邊.両長召抱人に同姓の沼尻愛次郎がいるが別人。

Watanobe, Watanobu or Watanobe. There is an Aijiro Numajiri with the same surname among the pages, but he is a different person.

天皇の御名と同姓なのは畏れ多いと大伴氏が判断したからだといわれている。

This was because the Otomo clan believed it was too presumptuous to have the same name as the Emperor.

現在では、同姓の分家との関係で用いられないかぎり、ほぼ「家元」の言いかえである。

Now, as long as it is not used when the branch sect shares the same surname, "Head of the School" is almost an equivalent saying to "originator of the sect".