Before Nikon made its first Camera in 1948 they were a supplier to Canon
of lenses and other optical parts. Nikon was actually called Nippon Kogaku
at that time and their lenses were Nikkors.
Most Canon rangefinders used a 39mm threaded mount, same as the early
Leicas and a number of other cameras. Nikon made Nikkor lenses in this
mount for Canon. Of course Canon made them too and so did other
manufacturers in Japan, Germany and the old USSR. The mount is known
as the M39 mount and you can find many lenses made for it. Other
cameras besides Canon and Leicas were also made that used this same
mount and they are loosely referred to as "Leica copies" though most
are not literally copies of Leicas, just similar in design with the same
lens mount.
In 1948 Nippon Kogaku began making rangefinder cameras of their own using
their own lenses with a different mount. These cameras were called
Nikons and eventually the company took 'Nikon' as their name and the Nippon
Kogaku name was dropped.