It's derived from the Greek words:
* Di- meaning "two"
* Proto- meaning "first"
* -donta meaning "teeth"
Therefore, Diprotodonta literally means "two-front-teeth".
This refers to the most defining characteristic of this order: having a pair of large, lower incisor teeth that protrude forward and are used for biting and chewing. These teeth are often quite prominent and are positioned in front of the other teeth.