identical twin
US /aɪˌden.tɪ.kəl ˈtwɪn/
UK /aɪˌden.tɪ.kəl ˈtwɪn/
1.
either of two fetuses or children born at the same birth who have developed from the same ovum and are therefore always of the same sex and usually very similar in appearance
:
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My cousins are identical twins; it's hard to tell them apart.
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She gave birth to a pair of healthy identical twins.