Translation guide
In Japanese, the word for twins depends on whether they are identical or fraternal, and there are also specific terms for twin siblings. The most common and general term is 双子.
Referring to two children born at the same time, without specifying type.
The most common and general word for twins. Can be used for both identical and fraternal twins, though it often implies fraternal twins in medical contexts.
彼女は双子を妊娠している。
She is pregnant with twins.
あの双子はとても似ている。
Those twins look very alike.
A more formal or medical term for twins. Often used in written contexts.
双生児の研究は遺伝学に貢献している。
Twin studies have contributed to genetics.
Twins that developed from a single fertilized egg and look exactly alike.
The precise medical term for identical twins. Often shortened to 一卵性 in conversation.
彼らは一卵性双生児なので、見分けがつかない。
They are identical twins, so I can't tell them apart.
A more common way to say identical twins, using the general word 双子 with the modifier 一卵性.
一卵性の双子はDNAが同じだ。
Identical twins have the same DNA.
Twins that developed from two separate eggs and may not look alike.
The precise medical term for fraternal twins. Often shortened to 二卵性 in conversation.
二卵性双生児は普通の兄弟と同じくらい似ている。
Fraternal twins are as similar as regular siblings.
A more common way to say fraternal twins, using the general word 双子 with the modifier 二卵性.
二卵性の双子は性別が異なることもある。
Fraternal twins can be of different sexes.
Referring to one person who is a twin.
Literally 'one of the twins'. Used to specify one twin when the pair is known.
双子の片方が医者になった。
One of the twins became a doctor.
Older twin brother. Similarly, 双子の弟 (younger twin brother), 双子の姉 (older twin sister), 双子の妹 (younger twin sister).
私の双子の兄は東京に住んでいる。
My twin brother lives in Tokyo.
双子 is the everyday word for twins. 双生児 is more formal and often used in medical or academic contexts. In casual conversation, 双子 is always preferred.
When referring to your own twin sibling, use the appropriate family term: 兄 (older brother), 弟 (younger brother), 姉 (older sister), 妹 (younger sister) with 双子の. For example, 双子の妹 means 'my younger twin sister'.