There are a few conjectures as to what the D  stands for. Some have said it is an abbreviation for departure  or decision.  Others claim that it stands for doomsday.  However, according to the United States military, the origin of the popular nickname has more to do with their terminology.

The word for tiger in Italian is the feminine noun tigre (plural: tigri) which derives from the Latin tigris. It remains feminine regardless of whether you are talking about a male tiger (una tigre maschio) or a female tiger (una tigre femmina).

A tigress is a female tiger.