What is Duplicate?
Duplicate is which is a copy Put the duplicate invoices in the file. Synonym identical (noun) a copy She sent the invoice and filed the duplicate. Antonym original (verb) to make a copy of a document such as a letter She duplicated the letter and put the copy into a file. you are just duplicating his work you are just doing the same work as he did earlier
source: Easier English, Student Dictionary Upper Intermediate Level