What does 'Mitsubishi' mean?

Mitsubishi is the Japanese words for three diamonds.

The name Mitsubishi (三菱) has two parts: "mitsu" meaning "three" and "hishi" (which becomes "bishi" in the middle of a word) meaning "water caltrop" (also called "water chestnut"), and hence "rhombus", which is reflected in the company's famous logo. It is also translated as "three diamonds".