Double; twofold.

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

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.

To double; to fold; to render double.

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