also: そうし
noun
Refers either to the pair of children born from the same pregnancy or to one member of such a pair. Commonly used as 双子の兄, 双子の姉妹, 双子を産む, and similar expressions.
彼女は双子を産んだ。
She gave birth to twins.
私には双子の兄がいる。
I have an older twin brother.
双子でも性格は全然違う。
Even though they are twins, their personalities are completely different.