- a copy that corresponds to an original exactly
"he made a duplicate for the files"

- something additional of the same kind
"he always carried extras in case of an emergency"

- increase twofold
"The population doubled within 50 years"

- make or do or perform again
"He could never replicate his brilliant performance of the magic trick"

- make a duplicate or duplicates of
"Could you please duplicate this letter for me?"

- duplicate or match
"The polished surface twinned his face and chest in reverse"

- being two identical

- identically copied from an original
"a duplicate key"

1. Double; twofold.

Duplicate proportion
or ratio
(Math.), the proportion or ratio of squares. Thus, in geometrical proportion, the first term to the third is said to be in a duplicate ratio of the first to the second, or as its square is to the square of the second. Thus, in 2, 4, 8, 16, the ratio of 2 to 8 is a duplicate of that of 2 to 4, or as the square of 2 is to the square of 4.

1. That which exactly resembles or corresponds to something else; another, correspondent to the first; hence, a copy; a transcript; a counterpart.

"I send a duplicate both of it and my last dispatch." -- Sir W. Temple.

2. (Law) An original instrument repeated; a document which is the same as another in all essential particulars, and differing from a mere copy in having all the validity of an original. Burrill.

1. To double; to fold; to render double.

2. To make a duplicate of (something); to make a copy or transcript of. Glanvill.

3. (Biol.) To divide into two by natural growth or spontaneous action; as, infusoria duplicate themselves.