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twin (twĭn)
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n.
1. One of two offspring born at the same birth.
2. One of two identical or similar people, animals, or things; a counterpart.
3. twins Mineralogy Two interwoven crystals that are mirror images of each other.
4. A twin bed.
adj.
1. Being two or one of two offspring born at the same birth: twin sisters.
2. Being two or one of two identical or similar people, animals, or things: twin cities; a twin bed.
3. Botany Of or relating to structures, such as flowers, that occur in pairs.
4. Consisting of two identical or similar parts: a twin lamp fixture.
5. Being of a size that will fit a twin bed: twin sheets.
v. twinned, twin·ning, twins
v.intr.
1.
a. To give birth to twins.
b. Archaic To be one of twin offspring.
2. To be paired or coupled.
v.tr.
1. To pair or couple.
2. To provide a match or counterpart to.

[Middle English, from Old English twinn, twofold; see dwo- in the Appendix of Indo-European roots.]

The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2018 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
 

Indo-European & Semitic Roots Appendices

    Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:

    Indo-European Roots

    Semitic Roots

    The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.

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