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-size bed.

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.

1. 1. To give birth to twins.
   2. Archaic. To be one of twin offspring.
2. To be paired or coupled.

1. To pair or couple.
2. To provide a match or counterpart to.

[Middle English, from Old English twinn, twofold.]

The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.