Insatiable (adjective)

1. Not able to be satisfied or appeased.
2. Having an endless or constant desire for something.

Origin:

From the latin word "insatiabilis" which means "not capable of being satisfied".

Examples:

1. His appetite for food was insatiable.
2. Her desire for success was insatiable.
3. The insatiable hunger of the monster could not be satisfied.
4. His thirst for power was insatiable.
5. Her need for attention was insatiable.