copy-keymap is a built-in function in `C source code'.

(copy-keymap KEYMAP)

Return a copy of the keymap KEYMAP.
The copy starts out with the same definitions of KEYMAP,
but changing either the copy or KEYMAP does not affect the other.
Any key definitions that are subkeymaps are recursively copied.
However, a key definition which is a symbol whose definition is a keymap
is not copied.