The Japanese words for three diamonds represent the name of which large manufacturer?

The name "Mitsubishi" refers to the three-diamond emblem. "Mitsubishi" is a combination of the words mitsu and hishi. Mitsu means three.
Hishi means water chestnut, and Japanese have used the word for a long time to denote a rhombus or diamond shape. Japanese often bend the "h" sound to a "b" sound when it occurs in the middle of a word. So they pronounce the combination of mitsu and hishi as mitsubishi.