Eternity (noun)

1. An infinite or immeasurably long period of time.
2. The state or quality of being eternal.
3. The timeless and endless nature of existence.

Origin:

From the latin aeternitatem (eternity), from aeternus (eternal), from aevum (age).

Examples:

1. For him, waiting for her felt like an eternity.
2. The concept of eternity is difficult for the human mind to grasp.
3. The love they shared felt like it would last for eternity.
4. Eternity is a fundamental part of many religious beliefs.
5. The universe is thought to have existed for eternity.