As a verb:
* "I accidentally duplicated the file, so now I have two copies."
* "The company is trying to duplicate the success of its first product."
* "The artist refused to duplicate his famous painting."
As a noun:
* "I found a duplicate of the missing document in the filing cabinet."
* "The detective was looking for duplicates of the stolen artwork."
* "There were several duplicates of the same book on the shelf."
As an adjective:
* "This is a duplicate key, so you can use it to open the door."
* "The duplicate receipt proved that I had paid for the purchase."
* "The software came with a duplicate installation disk."
The meaning of "duplicate" will depend on the context of the sentence.