noun
double, second, mate, match, twin, copy, facsimile, replica, reproduction, photocopy, carbon, carbon copy, ditto, likeness, counterpart, counterfeit, analogue, second edition, parallel, correlate, repetition, duplication, recurrence, Xerox (trademark), look-alike, chip off the old block*, ringer*, dead ringer*, clone*; see also copy, imitation 2, reproduction 2.
Antonyms original*, pattern, prototype.
in duplicate