adjective / noun
covert
KOH-vurt/ˈkəʊvɜːrt/
Concealed from ordinary view.
The woman keeps a covert watch on the meeting from behind a curtain.

Etymology
The French verb supplied a participle literally meaning “covered.” Something covered is screened from sight, giving the word its sense of hidden or secret.
In context
The Spanish Inquisition is famous for public trials and burnings. But most people don't know about the covert operatives the Inquisition employed to eliminate enemies who could not be prosecuted publicly.
More examples
- The agency conducts a covert investigation into the missing funds.
- She casts a covert glance at her watch.
- The rabbit disappears into a covert of thick brush.
Forms
covert · coverts
covertly adverb — In a secret or hidden manner.