Why is the name “Spartan” used?

The word “spartan” means self-restrained, simple, frugal and austere. In the fifth century BC, the best and most feared soldiers in Greece were Spartan warriors, noted for their professionalism. The Spartans were widely regarded as having the best soldiers and the strongest army of any city-state in Ancient Greece. From the moment they were born, every Spartan male underwent rigorous training to become a warrior.