The word sashimi means “pierced body”, i.e. “刺身 = sashimi, where 刺し = sashi (pierced, stuck) and 身 = mi (body, meat). The culture of eating raw fish started in China as early as 500 BCE and the delicacy arrived in Japan during the Heian Period.  This word dates from the Muromachi period, and was possibly coined when the word “切る = kiru (cut), the culinary step, was considered too inauspicious to be used by anyone other than samurai. This word may derive from the culinary practice of sticking the fish’s tail and fin to the slices in identifying the fish being eaten.
Another possibility for the name could come from the traditional method of harvesting. ‘Sashimi Grade’ fish is caught by individual handline. As soon as the fish is landed, its brain is pierced with a sharp spike; and it is placed in slurried ice. This spiking is called the Ike jime process, and the instantaneous death means that the fish’s flesh contains a minimal amount of lactic acid. This means that the fish will keep fresh on ice for about ten days, without turning white or otherwise degrading.
Many non-Japanese use the terms sashimi and sushi interchangeably, but the two dishes are distinct and separate. Sushi refers to any dish made with vinegared rice. While raw fish is one traditional sushi ingredient, many sushi dishes contain seafood that has been cooked, and others have no seafood at all.