When mammals have two babies at once, each of them is a twin. If you have a twin brother or sister, the two of you are always the same age.

There are identical twins, who have the same DNA, and fraternal twins, who are more like two siblings who happen to be born at the same time. It's more common to describe humans as twins than other animals. The adjective twin can also describe a pair of things, like the twin chocolate cakes you serve at your birthday party or the "Twin Cities" in Minnesota, Minneapolis and St. Paul.

Definitions of twin
  1. noun
    either of two offspring born at the same time from the same pregnancy
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    dizygotic twin, fraternal twin
    either of two twins who developed from two separate fertilized eggs
    identical twin, monozygotic twin, monozygous twin
    either of two twins developed from the same fertilized ovum (having the same genetic material)
    Siamese twin, conjoined twin
    one of a pair of identical twins born with their bodies joined at some point
    type of:
    sib, sibling
    a person's brother or sister
  2. noun
    a duplicate copy
    synonyms: counterpart, similitude
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    type of:
    duplicate, duplication
    a copy that corresponds to an original exactly
  3. adjective
    being two identical
    synonyms: duplicate, matching, twinned
    going well together; possessing harmonizing qualities
  4. verb
    give birth to twins
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    type of:
    bear, birth, deliver, give birth, have
    cause to be born
  5. verb
    grow as twins
    twin crystals”
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    type of:
    increase in size by natural process
  6. verb
    bring two objects, ideas, or people together
    synonyms: couple, match, mate, pair
    give or join in marriage
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    provide with an unsuitable mate
    match badly; match two objects or people that do not go together
    type of:
    bring together, join
    cause to become joined or linked
  7. verb
    duplicate or match
    “The polished surface twinned his face and chest in reverse”
    synonyms: duplicate, parallel
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    type of:
    agree, check, correspond, fit, gibe, jibe, match, tally
    be compatible, similar, or consistent; coincide in their characteristics
Word Family

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