WordNet sense 1 (something additional of the same kind):

extra

WordNet sense 2 (a copy that corresponds to an original exactly):

duplication

WordNet sense 3 (duplicate or match):

parallel, twin

WordNet sense 4 (closely similar or comparable in kind or quality or quantity or degree):

same

WordNet sense 5 (make or do or perform again):

double, repeat, replicate, reduplicate

WordNet sense 6 (being two identical):

matching, twinned

WordNet sense 7 (going well together; possessing harmonizing qualities):

matched