Webster's Revised Unabridged Dictionary · 1913

duplicate

duplicate , adjective

[Latin duplicatus, past participle of duplicare to double, from duplex double, twofold. See Duplex.]

Double; twofold.
Collocations (1)
Duplicate proportion or Duplicate ratio (Mathematics) , 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.

Duplicate , noun

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

Duplicate , transitive verb

1.
To double; to fold; to render double.
2.
To make a duplicate of (something); to make a copy or transcript of. — Glanvill
3.
(Biology) To divide into two by natural growth or spontaneous action; as, infusoria duplicate themselves.