Invisible (adjective)

1. Not able to be seen.
2. Not noticed or attracting attention.
3. Intangible or not having a physical form.

Origin:

Late middle english, from old french, from latin invisibilis, from in- + visibilis visible.

Examples:

1. The thief used an invisibility cloak to escape unnoticed.
2. The stars were invisible in the light-polluted city.
3. The work of the cleaners was invisible as they kept the office spotless.
4. The effects of the disease are often invisible, making it difficult to diagnose.
5. The invisible wind caused the leaves to rustle, even though the air was still.