The name Constantin is a boy's name of French, Latin origin meaning "steadfast". Constantin and discussed in our forums with posts like "Best name or combo from previous poster's signature!".
From the experts:
More likely to be spelled Constantine, this was the name of the first Christian emperor of the Roman empire, as well as three Scottish kings. Previously thought of as too bulky and unwieldy a name for a modern child, these days it would be perfectly acceptable.