Covert (adjective)

1. Not openly acknowledged or displayed; hidden or disguised.
2. Done in secret or without the knowledge of others.
3. Not open or public.

Origin:

The word covert comes from the old french word "covrir" which means "to cover" and it first appeared in the english language in the 14th century.

Examples:

1. The operation was conducted on a covert basis.
2. He had a covert agenda and worked behind the scenes to achieve it.
3. The company had a covert program to spy on its competitors.
4. The government had a covert plan to infiltrate the terrorist group.
5. The organization was involved in covert activities.