The Kamehameha is the most famous attack in all of Dragonball/Z/GT. But when Akira Toriyama was trying to think up a name for Kame-Sennin's move in early Dragonball, it was in fact his wife who came to the rescue and said "What about Kamehameha?".
The fact is that Kamehameha was actually a real person! A king no less! King Kamehameha I, or Kamehameha the Great, was King of Hawaii from 1758 to 1819. He was born just after Haley's Comet appered, which proficised his great rule. He succeededin untiting all the Hawaiian islands iunder his rule in 1810, and founded the Kamehameha dynstay, lasting till Kamehameha V, who died in 1872. The name Kamehameha means "The Very Lonely One" or "The One Set Apart" He was a powerful king who amassed a fortune through trade and also maintained the islands' indipendance from European explorers, something his successors found too much to handle. Today his name lives in the hearts and minds of the Hawaiian people, and also in the hearts and minds of Dragonball Z fans.
This was created to try and educate Dragonball Z fans as to the origins of Dragonball Z's most famous attack.