n.
Function: adjective
Etymology: Middle English, twofold, double, from Old English twinn; akin to Old Norse tvinnr two by two, Old English tw ā two
Date: 1593
1 : born with one other or as a pair at one birth <my twin brother> < twin girls>
2 a : made up of two similar, related, or connected members or parts : DOUBLE b : paired in a close or necessary relationship : MATCHING c : having or consisting of two identical units d : being one of a pair