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. In Japanese, the "h" sound is often pronounced as a "b" when it occurs in the middle of a word. So they pronounce the combination of mitsu and hishi as mitsubishi.

Yataro Iwasaki, the founder of the first Mitsubishi organization, chose the three-diamond mark as the emblem for his company. The mark is suggestive of the three-leaf crest of the Tosa Clan, Yataro's first employer, and also of the three stacked rhombuses of the Iwasaki family crest.

-- https://www.mitsubishi.com/en/profile/group/mark/