弟おとうと息子むすこ

also: おとむすこ

Meanings

younger son

Refers specifically to a younger son, as opposed to an older son or a younger brother. Not a common everyday word; more often seen in literary or explanatory contexts.

彼かれは三さん人にん兄きょう弟だいの弟おとうと息子むすこだ。
He is the younger son among three brothers.
弟おとうと息子むすこはまだ学がく生せいで、兄あにはもう働はたらいている。
The younger son is still a student, while the older brother is already working.