adjective

1. 1. consisting of or being two separate but similar or closely related things; forming a pair; double; paired twin beds
   2. being one of a pair of such things; being a counterpart
2. 1. being two offspring from the same pregnancy twin girls
   2. being either one of two offspring from the same pregnancy a twin sister

Etymology: ME < OE twinn & ON tvinnr, double, both < base of two

noun

1. either one of two offspring from the same pregnancy: twins are either identical (produced from the same ovum) or fraternal (produced from separate ova)
2. either one of two persons or things very much alike in appearance, shape, structure, etc.
3. a compound crystal of two crystals or parts having a common face but in reversed positions with respect to each other

intransitive verb twinned, twinning twin′·ning

1. to give birth to twins
2. to be paired or coupled (with another)
3. Archaic to be born at the same birth

transitive verb

1. to give birth to as twins
2. to be or provide a counterpart to
3. to pair or couple